Velouté de poireaux

03 — Method

1. Trim the 1 kg (2.2 lb) of leek whites, removing the green leaves and roots. Cut a 3 cm (1 in) cross into the base to make rinsing easier — dirt always collects between the tight layers and has to go.
2. Rinse the leeks well under cold water, gently spreading the layers with your fingers to wash out all the hidden dirt. This is ABSOLUTELY essential — nobody wants grit in their soup.
3. Peel the yellow onion and thinly slice it into half-moons. Peel the 400 g (14 oz) of potatoes and cut into even 2 cm (¾ in) cubes so they cook at the same pace as the leeks. Slice the leeks into 5 mm (¼ in) rounds.
4. Melt the unsalted butter in the large saucepan over medium heat without browning. Soften the onion for 5 minutes until translucent. Add the leeks, cover and cook over low heat for 10 minutes until soft.
5. Add the potatoes and pour in hot chicken stock to just cover. Season with fleur de sel and plenty of pepper. Bring to a simmer and cook over low heat for 25 minutes until the vegetables are very soft.
6. Blend the soup right in the pan with an immersion blender until perfectly smooth and velvety. If it’s too thick, add a little hot whole milk to loosen it.
7. Stir in the thick crème fraîche, the whole milk and the pinch of freshly grated nutmeg. Cook 3 minutes over low heat, stirring with a wooden spoon. Adjust the salt and pepper to taste.
8. Finely chop the chives, keeping a few whole stems to garnish. Serve the soup piping hot in deep bowls, sprinkled with chives and finished with a swirl of crème fraîche.