Wash potatoes thoroughly and cook in boiling water for about 20 minutes. Drain the potatoes, rinse, peel and let the potatoes cool down well. Wash and clean the cucumber. Cut cucumber lengthwise in half, remove seeds. Cut cucumber into pieces. Clean, wash and halve the radishes.
Peel and finely dice onion. Wash fish, dab dry and cut into pieces. Heat oil in a large pan. Fry the fish pieces for 2-3 minutes, turning them carefully, and take them out. Season with salt and pepper. Fry cucumber pieces and radishes over medium heat for about 6 minutes, turning them over. After 4 minutes add onion. Add stock, white wine and mustard and simmer for about 4 minutes. Wash and finely chop the dill. Stir cream and sauce thickener into the ragout. Add fish pieces to the ragout and fill into a greased casserole dish. Grate the potatoes.
Add stock, white wine and mustard and simmer for about 4 minutes. Wash and finely chop the dill. Stir cream and sauce thickener into the ragout. Add fish pieces to the ragout and fill into a greased casserole dish. Grate the potatoes. Season the grated potatoes with salt and nutmeg. Spread on the ragout and sprinkle with butter in flakes. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for about 35 minutes, remove from oven
waiting time approx. 2 hours