It is better to cook 4-6 servings at once in a big square pan and then split into pieces like a pie.
Remove fish bones from the fillet, process the fillet in a food processor with S-shaped knife.
Chop the onion, grate the carrot into strips.
Sauté the vegetables until they are nice and soft, and then leave them to cool down.
Put ½ of the fish fillet in a casserole dish, top it with the vegetables, then top it all off with the rest of the fillet. (If you are lazy, just mix the fillet and the vegetables and put it all in a casserole dish). Coat it with some sour crème.