Peel and wash the carrots and cut them into fine slices. Peel onions, cut into rings. Wash potatoes, also cut into thin slices. Fry onions and potatoes in hot oil first, salt a little.
Add carrots, deglaze with 100 ml water and steam for about 5 minutes. In the meantime wash the fish fillet, dab dry and cut into pieces. Sprinkle with lemon juice, salt. Crush peppercorns.
Crumble toast finely and mix with soft butter, sour cream and crushed pepper. Put the vegetables in a suitable, flat casserole dish. Place fish on top. Spread pepper butter evenly on top.
Bake in the preheated oven (electric oven: 200 °C/ gas: level 3) for 20-25 minutes. Serve garnished with fresh herbs.