Wash the leek and cut into pieces about 1 cm in size and cut the onion into small pieces. Put the butter in a saucepan, sauté the leek and the chopped onion until translucent. Dust with flour and deglaze with the white wine and stock. Let simmer for about 25 minutes. Then puree with the blender and pass through a hair sieve. Add the cream and simmer for another 10 minutes. Season to taste with salt, pepper and nutmeg. Remove the crust from 4 slices of toast and cut into cubes. Heat fresh butter in a pan and roast the toast cubes until golden brown.