Delia Smith Leek, Onion & Potato Soup Recipe

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Delia Smith’s leek, onion and potato soup is a straightforward vegetable soup built around a small group of everyday ingredients. Leeks, onion and potatoes are gently cooked in butter before vegetable stock and milk are added, then the soup is blended until smooth. The finished soup can be served warm with cream or crème fraîche and fresh herbs.

Delia developed this soup for The Delia Collection: Soup, part of her wider Vegetarian Collection, and it has remained one of her most requested recipes ever since. Serve it hot as a starter or light lunch, or chill it down and you’ve essentially made a homely version of vichyssoise.

Why You’ll Love This Soup

This is the kind of soup that rewards simple cooking rather than a long ingredient list.

• Creamy without needing a thickener: potatoes provide body as they cook and are blended.
• Gentle flavour: leek and onion give the soup savoury depth without overpowering the potato.
• One-pot cooking: the vegetables are cooked in the same saucepan as the soup.
• Good for different seasons: serve it hot on a cold day or chilled when you want something lighter.
• Easy to prepare ahead: the soup can be made in advance and gently reheated.
• Flexible serving style: crème fraîche, cream, chives or parsley can be used to finish each bowl.

Ingredients You’ll Need

This larger batch serves approximately 8 people.

• 6 large leeks, trimmed and finely sliced
• 2 medium onions, finely chopped
• 3 medium potatoes, peeled and diced
• 75g butter (2.6 oz)
• 1.3 litres vegetable stock (45.8 fl oz)
• 400ml whole milk (13.5 fl oz)
• Salt, to taste
• Freshly milled black pepper, to taste

To serve

• 3 tablespoons cream or crème fraîche
• 2 tablespoons freshly snipped chives or chopped fresh parsley

How to Make Delia Smith Leek Onion and Potato Soup

1. Prepare and wash the leeks

Remove the tough outer layer from the leeks and trim away the root ends. Split each leek lengthways, slice it finely and wash the pieces thoroughly in several changes of water.

Drain them well. Excess water is not helpful when the vegetables are being gently sweated, so give the sliced leeks time to drain before cooking.

2. Sweat the vegetables in butter

Melt the butter in a large, heavy-based saucepan over a very low heat. Add the sliced leeks, chopped onions and diced potatoes.

Season with salt and freshly milled black pepper, then stir so the vegetables are coated with the butter.

Cover the pan and cook gently for about 15 minutes. The vegetables should soften rather than brown. If they begin catching on the base of the pan, reduce the heat further.

3. Add the stock and milk

Pour in the vegetable stock and milk. Bring the mixture carefully to simmering point, then reduce the heat.

Cover the pan and cook gently for approximately 20 minutes, or until the potatoes and leeks are completely tender.

Avoid a vigorous boil. Because milk is part of the liquid, excessive heat can cause the soup to rise and boil over.

4. Blend until smooth

Take the saucepan off the heat and allow the soup to cool slightly before blending.

Transfer the soup to a blender in manageable batches if necessary. Blend until smooth and creamy, taking care with the hot liquid.

If using a stick blender, work carefully and keep the blade fully immersed to reduce splashing.

5. Reheat and adjust the seasoning

Return the blended soup to the saucepan. Warm it gently rather than bringing it to a hard boil.

Taste and adjust the salt and pepper. The exact amount required will depend partly on the vegetable stock you use, so seasoning at this stage is important.

6. Finish and serve

Ladle the hot soup into bowls and add a small swirl of cream or crème fraîche.

Finish with freshly snipped chives or chopped parsley. Serve immediately with bread if desired.

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Tips for Making the Soup Successfully

Wash the leeks properly

This is one of the most important preparation steps. Soil and grit can sit deep between the leek layers. Slicing them before washing makes it easier to remove anything trapped inside.

Keep the first stage gentle

The vegetables should soften in the butter rather than develop a deep fried or caramelised flavour. A low temperature helps preserve the delicate leek flavour.

Dice the potatoes evenly

Try to keep the potato pieces reasonably similar in size. This helps them become tender at roughly the same time.

Don’t boil the milk aggressively

Once the stock and milk have been added, maintain a gentle simmer. A hard boil is unnecessary and increases the risk of the milk bubbling over.

Blend carefully

Hot soup can be dangerous in a sealed blender because steam builds pressure. Let the soup cool slightly and follow your blender manufacturer’s instructions for hot liquids.

Season at the end

Stock can vary considerably in saltiness. Tasting after blending gives you a much better idea of how much additional seasoning the soup needs.

Recipe Variations and Substitutions

The recipe above follows the core ingredients of Delia Smith’s original. The following are optional adaptations rather than changes to the original recipe.

Make it vegetarian

The recipe is already vegetarian. Use a vegetable stock that is suitable for your dietary requirements.

Make it dairy-free

For a dairy-free adaptation, you would need to replace both the butter and milk with suitable alternatives. This will produce a different flavour and texture, so it should be regarded as an adaptation rather than the original recipe.

Make it thicker

If you prefer a particularly thick soup, use slightly less liquid when making an adapted batch. It is better to adjust consistency gradually than to remove too much liquid at the beginning.

Serve it chilled

The chilled version is a classic vichyssoise-style preparation.

For a chilled version, allow the blended soup to cool safely before refrigerating, then serve cold with the garnish of your choice.

What to Serve With Leek, Onion and Potato Soup

A simple soup benefits from something crisp or chewy alongside it.

Good choices include:

• Crusty white bread
• Sourdough
• Wholemeal bread
• Toasted baguette
• A simple green salad
• Cheese and bread for a more substantial lunch

If serving the soup as a starter, keep the accompaniment modest. A small piece of crusty bread is enough because the potato makes the soup more substantial than many clear vegetable soups.

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For a light lunch, pair a generous bowl with a fresh salad. For dinner, the soup also works well before a substantial homemade main course such as cottage pie or chicken Basque.

For a meal centred around fish, cod mornay can follow the soup as a richer main course.

On a cold night, follow it with something heartier like Slow Cooker Chicken Casserole

Nutrition Information

The following figures are approximate estimates per serving, based on the adjusted eight-serving recipe and typical values for the ingredients. Actual nutrition will vary according to the type of vegetable stock, milk, butter and cream used.

Nutrient	Approx. per serving
Calories	210 kcal
Protein	5 g
Carbohydrates	28 g
Fat	9 g
Fibre	4 g
Sugar	6 g
Salt	Varies

Dietary Information

This Delia Smith leek, onion and potato soup is naturally vegetarian and can easily be adapted for other diets.

• Gluten-free: Yes, as long as you use gluten-free vegetable stock.
• Vegetarian: Yes, the original recipe is vegetarian.
• Vegan: No, because it contains butter and milk. Replace the butter with vegan butter or oil and the milk with unsweetened plant-based milk.
• Dairy-free: No, but you can replace the butter and milk with dairy-free alternatives and skip the cream garnish.

The potatoes help make the soup naturally thick and creamy, so you don’t need flour or another thickener.

Can You Make This Recipe Ahead?

Yes. Leek, onion and potato soup is well suited to preparing ahead because the vegetables are cooked, blended and reheated as part of the same process.

For the best result, make the soup through the blending stage, cool it appropriately and refrigerate it in a covered container. Reheat it gently on the hob before serving.

Add the cream or crème fraîche and fresh herbs shortly before serving rather than mixing the garnish into the whole batch.

If the soup becomes thicker after chilling, loosen it with a small amount of milk or stock while reheating.

Storage and Reheating

Allow cooked soup to cool appropriately before transferring it to a clean, covered container and refrigerating it.

Reheat gently in a saucepan over low heat, stirring regularly, until piping hot throughout. If frozen, defrost fully in the fridge overnight first. Avoid reheating and refreezing multiple times, as the texture can turn watery with repeated temperature changes.

For freezing, portion the soup into suitable freezer containers and leave enough room for expansion. Defrost thoroughly in the refrigerator before reheating, then warm slowly and stir well.

The texture can sometimes change slightly after freezing and thawing. If it looks less smooth, gentle reheating followed by careful stirring or blending can help restore its consistency.

Add fresh herbs and the cream or crème fraîche garnish after reheating for the best presentation.

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Meal Prep

This soup works particularly well for meal preparation.

Make a full batch, divide it into individual portions and store the portions appropriately. Keeping the garnish separate means each serving can be finished just before eating.

For packed lunches, use leak-proof containers designed for liquids. If reheating at work, follow the instructions for your appliance and make sure the soup is heated thoroughly.

The simplest meal-prep combination is soup plus bread, while a small salad can add freshness when serving it at home.

Common Cooking Mistakes to Avoid

• Skipping the leek-washing step. Leeks trap soil between their layers, and it doesn’t cook out — it just gets blended into the soup. Always rinse thoroughly in changed water.
• Cooking the vegetables too fast during the sweating stage. High heat browns them, changing the flavour from sweet and mellow to something closer to caramelised onion soup.
• Letting the milk boil hard. Once milk is in the pan, a rolling boil risks it splitting or boiling over the sides.
• Under-seasoning. Potato and milk both mute seasoning, so this soup usually needs a more generous pinch of salt than you’d expect.

Frequently Asked Questions

Can I freeze leek, onion and potato soup?

Yes, the soup can be frozen. Freeze it in suitable portions, thaw it safely and reheat gently. The texture may change slightly after freezing, so stir thoroughly during reheating.

Can I serve this soup cold?

Yes. The chilled version works as a classic vichyssoise-style soup. Allow it to cool safely before refrigerating and serving.

How do I know when the vegetables are cooked?

The potatoes and leeks should be completely tender when tested with a knife. If the potato still offers noticeable resistance, give the soup a little more gentle cooking time before blending.

Why is my leek and potato soup too thick?

Potatoes absorb liquid and the soup can become thicker as it cools. Add a little milk or vegetable stock while reheating until the consistency is where you want it.

Why does my soup taste bland?

Check the seasoning after blending. Potato and milk can soften the perception of salt, while different vegetable stocks contain different amounts of seasoning. Add salt and freshly milled black pepper gradually and taste as you go.

Can I make this soup without cream?

Yes. Cream or crème fraîche is used as a finishing garnish rather than as the main liquid, so the soup can be served without it. The result will simply be slightly less rich.

Can I double the recipe?

Yes, provided you use a saucepan large enough to hold the increased volume safely. Keep the ingredient proportions consistent and allow enough time for the larger quantity of vegetables to become completely tender.

Conclusion

Delia Smith’s leek, onion and potato soup is a useful recipe to keep in your repertoire when you want a smooth, warming soup without complicated preparation. The combination of gently cooked leeks, onion and potato gives it plenty of character, while blending creates a naturally creamy texture.

Serve it hot with a swirl of crème fraîche and fresh chives for a simple starter or lunch, or chill it for a classic cold-soup variation. It is straightforward enough for everyday cooking and substantial enough to prepare as a make-ahead meal.