Leek, Potato and Arugula Potage with Butter

This potage begins with a very classic French preparation: a simple leek and potato soup, cooked slowly until completely tender and then blended to a smooth consistency.

Building on that traditional base, this version adds arugula, which brings a fresh, slightly peppery, vegetal note. Watercress is very common in this type of French soup, but arugula works beautifully when fresh watercress is difficult to find.

Another essential part of the recipe is the finishing touch of butter. It is not added simply for richness: stirred in at the end, off the heat, it softens the vegetal flavors, rounds out the soup and gives it a silkier, glossier texture. In this recipe, that final step is fundamental to the character of the potage.

The result is a simple yet elegant soup made from only a few ingredients, with a clean flavor in which the leek, potato and arugula remain clearly recognizable.

Serves: 2
Prep time: 10 minutes
Cooking time: about 45 minutes

Ingredients

• 250 g potato, peeled
• 180 g cleaned leek, including a little of the tender green part
• 600 ml water
• ¾ teaspoon salt, or to taste
• 50–60 g fresh arugula
• 25 g unsalted butter
• A little freshly ground black or white pepper, optional
• A few fresh arugula leaves, for serving

Method

1. Prepare the vegetables. Cut the potato into small cubes. Split the leek lengthwise and wash carefully between the layers to remove any grit, then slice thinly.
2. Cook the soup base. Place the potato, leek, water and salt in a saucepan. Bring to a boil, then reduce the heat. Cook partially covered for about 40 minutes, until the potato and leek are completely tender.
3. Add the arugula. Wash the arugula well and reserve a few leaves for serving. Add the rest to the soup and cook for only 2–3 minutes over low heat. Arugula cooks very quickly, so avoid cooking it too long or it may lose freshness and become overly bitter.
4. Blend. Blend until smooth and creamy. If using a Thermomix®, carefully transfer the hot soup to the mixing bowl and blend for about 30 seconds, gradually increasing from speed 5 to 8.
5. Adjust the consistency. Check the texture. If you prefer a slightly lighter soup, add 30–60 ml hot water and blend again. Taste and adjust the salt if necessary.
6. Finish with butter. Remove the soup from the heat and add the 25 g butter. Stir until fully incorporated and the soup becomes smoother, silkier and glossy. In a Thermomix®, mix for about 20 seconds / speed 3, no heat. Do not bring the soup back to a boil after adding the butter.
7. Serve. Serve immediately in deep plates or bowls. Finish with a few fresh arugula leaves in the center, using only a small amount so the green, creamy surface of the soup remains visible.

If you can find watercress

This soup can also be prepared with watercress, a very classic choice for this style of potage.

If you have fresh watercress, use about 60–70 g instead of the arugula and let it cook for about 5 minutes before blending.

Ingredient notes

If watercress is difficult to find where you live, fresh arugula is an easy and very successful substitute.

For the potato, choose a floury or starchy variety when possible, as it helps give the soup an especially creamy texture.