Grate cheese. Melt the fat. Dust flour on it and mix well. Stir in milk and stock and let it boil down a bit. Sprinkle in 25 g cheese while stirring, season with salt and pepper.
Wash the chicken filet, dab dry and cut into strips. Clean and halve the mushrooms. Clean and wash spring onions, dab dry and slice diagonally. Heat oil in a pan.
Sauté the meat in it. Add the mushrooms and fry. Season with salt and pepper. Cook for 5 minutes and deglaze with white wine. Let it boil down briefly. Put the chicken, mushrooms and spring onions in an ovenproof dish.
Add the sauce and sprinkle with the rest of the cheese. Bake in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for 10 minutes.