Blanch the sprouts in boiling water for 3 minutes and drain. Heat the butter in a large pan, add the sprouts and shake and toss them in the butter. Sprinkle over the flour and garlic, mix well and pour over the hot stock, stirring continually. Simmer until the sprouts are soft, about 20 minutes. Blend the soup until smooth.
Beat the egg yolk with the cream, pour a ladleful of sou