Rinse fish fillet, dab dry, cut into 8 pieces. Season with salt, pepper and lemon juice and put aside covered for about 20 minutes. Peel, wash and halve the potatoes and cook in boiling salted water for about 15 minutes. For the sauce, melt the fat, stir in the flour and sauté for about 1 minute. Add 250 ml broth and milk while stirring continuously, bring to the boil.
Stir in mustard. Season with salt and pepper, let it boil down a bit. In the meantime peel, wash and slice carrots diagonally. Peel garlic and chop finely. Heat 1 tablespoon of oil in a frying pan, fry the carrots and garlic in it. Add 125 ml broth and simmer for about 5 minutes. Season with salt, pepper and 1 pinch of sugar. Heat 2 tablespoons of oil in a frying pan and fry the fish fillets for about 5 minutes on each side. Drain the potatoes. Wash parsley, dab dry and chop finely.
Season with salt, pepper and 1 pinch of sugar. Heat 2 tablespoons of oil in a frying pan and fry the fish fillets for about 5 minutes on each side. Drain the potatoes. Wash parsley, dab dry and chop finely. Stir parsley into the carrots. Arrange pike-perch with carrots, potatoes and sauce. Serve garnished with parsley