Slice the onions and crush the garlic cloves then cover the oven pan bottom with them add salt and pepper (as much as you like) squeeze some lemon juice on the top, when you have done that cover these ingridients with perch filet. Then add salt, pepper and lemon juice to the filet and now cover the top again with onion slices and garlic. When you have done all abovementioned its time to make a sauce before cooking to top everything up. For sauce take the mayonnaise, egg yolk and cognac/brandy mix the ingridients well and pour on top of the onions, garlic and filet in the oven pan to nicely cover all up.....Now its time to start cooking.
Heat the oven to 180°C put the oven pan in and cook about 20-25 minutes. When ready serve with nice boiled yellow curry rice.