Clean the mushrooms and cut them into small pieces. Finely dice the onion. Cut the cucumber into thin strips.
Heat 20 g butter and fry the mushrooms and onions in it. Stir in the cream and sauce thickener, simmer for a few minutes. Add the cucumber strips and season the sauce with salt and pepper. Keep warm.
Season the schnitzel with salt and pepper. Turn in egg and breadcrumbs.
Heat the remaining butter in a second pan and fry the schnitzel in it for 2 - 3 minutes on each side.
Serve the schnitzel with the mushroom sauce. Garnish with parsley.