Leeks turn sweet and silky when they are cooked slowly, and floury potatoes give the soup its body without any cream. The only real work is washing the leeks well, because grit hides between the layers.

Blend the soup as smooth as you like it, then loosen with a little milk. Blend briefly: potatoes can turn gluey if they are worked too hard.

The recipe

Potato and leek soup

4 servings · 50 minutes total · Metric measurements

Ingredients

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Method

  1. Wash and slice the leeksTrim the leeks, slice them into thin rounds, and swish them in a bowl of cold water. Lift them out, leaving any grit behind, and drain.
  2. Soften the leeksMelt the butter in a large pot over medium-low heat. Add the leeks with a pinch of the salt. Cook gently for 8-10 minutes, stirring now and then, until very soft but not browned.
  3. Simmer the potatoesAdd the potatoes, stock, remaining salt, pepper and thyme. Bring to a simmer and cook for 18-20 minutes, until the potatoes are completely tender when pressed with a fork.
  4. BlendRemove the thyme sprigs. Add the milk, then blend until smooth, working in batches if needed. Take care with hot liquid: fill the blender no more than half full, hold the lid down with a folded tea towel, and start on a low speed.
  5. Season and serveReturn the soup to the pot and warm it through gently without boiling. Taste and adjust the salt, pepper and thickness with a splash of milk or stock.

Small details that help

  • Cook the leeks slowly. Browning them makes the soup darker and changes the flavour.
  • Blend briefly and stop as soon as the soup is smooth. Over-blending potatoes gives a sticky texture.
  • The soup thickens as it stands. Keep a little extra stock or milk nearby for reheating.

Swaps and variations

For a dairy-free soup, use olive oil and an unsweetened oat drink. Add a chopped carrot or a handful of spinach with the potatoes for a deeper flavour, or top each bowl with crisp cooked bacon if you eat meat.

What to serve with it

Ladle into warm bowls and serve with crusty bread. A swirl of cream, a few snipped chives or a little grated cheese all sit well on top.

Storage and reheating

Cool and refrigerate within 2 hours (1 hour above 32°C / 90°F) and use within 3 days. Reheat until steaming at 74°C / 165°F throughout. Freeze for up to 3 months; for the best texture, freeze before adding the milk and stir it in when reheating.

Food-safety reference: safe cooking and reheating temperatures. Refrigerate perishable food within 2 hours, or 1 hour above 32°C / 90°F. Keep the refrigerator at 4°C / 40°F or below.

Common questions

Can I freeze this soup?

Yes, for up to 3 months. It freezes best before the milk is added. Thaw overnight in the fridge, then reheat gently and stir in the milk.

Why did my soup turn gluey?

The potatoes were blended too long or at too high a speed. Next time, blend in short bursts and stop once smooth. A splash of hot stock can loosen a batch that has gone too far.

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