Preparing the cream of mâche

1. Sauté the mâche, onion, mushrooms, shallots, potatoes and leek greens in melted butter. 
2. Season with salt, then add 1 liter (4 cups) water and a bouillon cube. After 30 minutes, purée everything in a blender and correct the seasoning. 
3. Add the crème fraîche at the last minute. Whisk briskly: the cream of mâche is ready. 

Cooking the langoustines and presentation 

1. Roast the langoustine tails with no oil in a non-stick pan. 
2. Arrange them in bowls with some of the cream of mâche in the center. 
3. Garnish with mâche.