Peel and finely dice the onions and garlic. Heat 1 tablespoon of fat in a flat, wide saucepan. Fry the onion and garlic in it. Add spinach and 100 ml water. Cover and allow to defrost at low heat for about 15 minutes. Stir the spinach once.
Season with salt, pepper and nutmeg. In the meantime, bring cream and stock to the boil. Drain beetroot and dice finely. Add 2/3 of the beetroot to the cream, puree, bring to the boil and thicken with sauce thickener. Bring to the boil again and season to taste with salt and pepper. Sprinkle fish with lemon juice and season with salt and pepper. Heat oil in a pan and fry the carp fillets in it for 6-8 minutes while turning. Pour sauce onto preheated plates. Place the carp fillets on top. Arrange spinach on the fish. Sprinkle with remaining beetroot.
Sprinkle fish with lemon juice and season with salt and pepper. Heat oil in a pan and fry the carp fillets in it for 6-8 minutes while turning. Pour sauce onto preheated plates. Place the carp fillets on top. Arrange spinach on the fish. Sprinkle with remaining beetroot. Garnish with lemon and dill. Serve with boiled potatoes