For the cucumber soup with herbs, peel the cucumber, cut into thin slices, salt and leave covered. Then pour off the cucumber juice. Melt butter in a saucepan, add the cucumber slices and pour the stock.
During the 15 minutes of cooking, add more stock if necessary. Finally, add sorrel leaves, salt and cayenne pepper, thicken with a little stirred rice flour and remove from heat. Stir in the milk with the egg yolk and season the cucumber soup with herbs with lemon juice.