Wash the fish, pat dry and cut into 4 pieces. Sprinkle with lemon juice
Drain the beetroot well and cut it into small pieces. Bring 1/8 l water, milk, stock and 2/3 beetroot to the boil, simmer for about 2 minutes. Puree everything finely and bring to the boil again. Stir in cream and thicken with sauce thickener. Season to taste with salt and pepper
Peel and finely dice the onion and garlic. Sauté in 1 tbsp. hot fat. Steam spinach briefly. Season with salt, pepper and nutmeg. Pour on approx. 100 ml water, cover and steam for approx. 10 minutes
Season fish. Fry in 2 tablespoons of hot fat on each side for 3-4 minutes. Season spinach to taste. Arrange everything. Garnish with remaining beetroot, possibly lemon and dill. Serve with boiled potatoes