Heat the gnocchi for about 1 minute in boiling salted water. Grate cheese. Drain gnocchi and mix with cream and cheese. Pour into a greased casserole dish. Bake in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for approx. 15 minutes.
Peel onion and cut into rings. Wash and halve the tomatoes. Heat clarified butter in a pan. Fry onion rings in it until golden brown. Add the tomatoes, fry briefly. Season with salt and pepper.
Take the casserole out of the oven. Spread the onion and tomatoes on top.