# Potato Leek Soup

Potato leek soup is a silky, mild soup made with sweet leeks and tender potatoes. It has only a few ingredients, so each one matters, and the result is cozy and elegant.

Cook the leeks slowly in butter until they are completely soft, which brings out their sweetness. Blend it smooth, add a little cream, and top with chives for a simple, French-style soup.

- Total time: 45 min (prep 15 min, cook 30 min)
- Serves: 4
- Per serving (estimated): 300 kcal, 7 g protein
- Cuisine: French. Category: Soup. Diet: vegetarian, gluten-free.

## Ingredients

- 3 tbsp butter
- 3 large leeks, white and light green parts, sliced
- 2 cloves garlic, minced
- 700 g Yukon Gold potatoes, peeled and cubed
- 4 cups vegetable or chicken broth
- 2 sprigs fresh thyme
- 1 bay leaf
- 1/2 cup heavy cream
- 1 1/2 tsp salt
- 1/4 tsp white pepper
- 2 tbsp chopped chives

## Method

1. Slice the leeks in half lengthwise, then into half-moons. Rinse them well in a bowl of cold water to remove grit, then lift them out and drain.
2. Melt the butter in a large pot over medium-low heat. Add the leeks and 1/2 tsp salt. Cook 8 to 10 minutes, stirring, until completely soft but not browned.
3. Add the garlic and cook 30 seconds, until fragrant.
4. Add the potatoes, broth, thyme and bay leaf. Bring to a boil, then lower to a simmer, partly covered.
5. Cook 15 to 18 minutes, until the potato cubes break apart when pressed with a spoon.
6. Remove the thyme stems and bay leaf. Blend with an immersion blender until smooth, or work in batches in a blender, venting the lid.
7. Stir in the cream, the remaining 1 tsp salt and the white pepper. Warm over low heat for 2 minutes without boiling.
8. Taste, adjust the salt, and serve topped with chives.

## Why it works

- Cooking leeks gently in butter without browning brings out their sweetness and keeps the soup pale.
- Yukon Gold potatoes have medium starch, so they blend creamy without turning gluey.
- Blending releases starch from the potatoes, which thickens the soup with no flour needed.
- A small amount of cream rounds out the flavor so the soup tastes rich without being heavy.

## The science

- **Why leeks taste sweet.** Leeks are in the onion family and contain sulfur compounds that taste sharp when raw. Cooking them slowly over low heat breaks those compounds down and releases natural sugars, so the flavor turns mild and sweet. High heat would brown them and add bitterness.
- **Choosing the right potato.** Waxy potatoes hold their shape and starchy ones fall apart. Yukon Golds sit in the middle, so they soften enough to blend smooth but are less likely to turn gluey. Over-blending starchy potatoes can make the soup sticky and thick.

## Tips

- Rinse the sliced leeks in a bowl of water, because sand hides between the layers.
- Use an immersion blender and pulse briefly, since over-blending can make potato soup gluey.
- Use only the white and light green parts, which are tender and sweet.

## Mistakes to avoid

- Skipping the leek rinse: the soup tastes gritty, so soak and drain the slices.
- Browning the leeks: they turn bitter, so keep the heat at medium-low.
- Over-blending in a high-speed blender: the starch turns gummy, so blend just until smooth.

## Variations and swaps

- Serve it chilled the next day as vichyssoise, with extra chives.
- Top with crispy bacon or croutons for crunch.
- Stir in a handful of spinach before blending for a green soup.
- Swap heavy cream for whole milk or a splash of olive oil for a lighter soup.
- Swap the butter for olive oil and use vegetable broth to make it dairy-free.

## Storage

Refrigerate within 2 hours for up to 4 days. Freeze before adding the cream for up to 3 months, and reheat to 165°F (74°C).

## FAQ

**How do you clean leeks for soup?**

Cut them in half lengthwise, slice, and swish the pieces in a bowl of cold water. The grit sinks, so lift the leeks out and drain them.

**Which part of the leek do you use for soup?**

Use the white and light green parts, which are tender and sweet. The dark green tops are tough, though you can save them to flavor stock.

**What potatoes are best for potato leek soup?**

Yukon Gold potatoes are best because they blend creamy without turning gluey. Russets also work but can turn sticky if over-blended.

**Can I make potato leek soup without cream?**

Yes. The potatoes already make it creamy, so you can leave out the cream or use milk or a little olive oil.

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Source: https://cookingscientist.com/recipes/potato-leek-soup (Cooking Scientist). Learn the science of cooking in the Cooking Scientist app for iPhone and iPad: https://apps.apple.com/app/id6830326846