Clean the fish fillet, acidify, season with salt and pepper, place in a greased casserole dish.
Peel the vegetable onions, cut into medium-fine strips, sprinkle with hot oil in a pan and let them caramelize a little. Deglaze with wine and broth, simmer for 10-15 minutes. Stir in the sour cream, pepper and add a little salt if necessary.
Spread the mixture on the fish, sprinkle with cheese and bake in a preheated oven at 200 degrees for 20 minutes until golden brown. With baguette bread and white wine.