Peel the garlic and press it through a garlic press. Wash the thyme and remove the leaves from the stalks. Mix cream, garlic and thyme. Season with salt and pepper. Wash the fillets and dab dry.
Fry them in hot oil all around. Season with salt and pepper. Peel onions and cut into rings. Fry in the frying fat. Dust with flour and deglaze with the herb cream. Boil up briefly. Peel and wash the potatoes and carrots and slice them finely. Put the fillets, potatoes and carrots in an ovenproof dish. Mix onion cream with milk and spread on top.
Boil up briefly. Peel and wash the potatoes and carrots and slice them finely. Put the fillets, potatoes and carrots in an ovenproof dish. Mix onion cream with milk and spread on top. Cook in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for about 1 hour. Cut the fillet open and serve garnished with fresh herbs