Cut the onion into strips.
Grate the cheese on a coarse grater.
Cut the mushrooms into halves.
Cut the breast fillet into medium-sized pieces.
Cut the potatoes into slices.
Take a frying pan, grease it with sunflower oil and add the onion to fry.
Add mushrooms to the onions.
Fry until golden brown.
Take a baking dish, grease it with vegetable oil, and place the sliced potatoes in the dish.
Divide the grated cheese into 3 parts. Sprinkle a third of the cheese on top of the previously laid out potatoes.
Place fried mushrooms and onions on top.
Sprinkle the second portion of grated cheese on top.
Place the sliced breast fillet on top.
Pour cream over the casserole.
Sprinkle a third of the grated cheese on top. Add salt and ground black pepper to taste.
Place the dish in an oven preheated to 180 C for 1 hour, cook until golden brown.