Melt the butter in a frying pan with a bit of oil. When it has melted and the pan is very hot, start frying the large fillets, about 1.5-2 minutes on each side. Gently salt them. When the fillets turn "golden", remove from the pan and drizzle with lemon juice.
Pour a little oil into the same pan and fry the asparagus, onion and new potatoes cut into smaller pieces. When the contents of the pan have browned, add the chopped smaller flounder fillets and garlic. Stir for a while and pour in the cream, which you reduce to a thick sauce over low heat. At the end of the reduction add the dill, wild garlic and horseradish.
When the sauce is ready and is thick enough to your liking, turn off the gas and add salt to taste. Arrange the vegetables in a bowl (or on a flat plate if you like), place the flounder fillets on top and sprinkle with grated lemon zest.
Recipe by Wit Szychowski. Check out my fanpage "Pan Tasak".