The cleaned sorrel stew with a pinch of salt in sunflower oil for a few minutes. Triturated through a sieve. Prepare a light roux from the butter and flour, which is diluted with cold milk and add to pretritiya sorrel, boil, stirring, and season to taste with crushed garlic and ground pepper. Once puree boil a few minutes, add the grated feta cheese dish and retired from the fire. Sprinkle with chopped walnuts.