Cook the gnocchi in lightly boiling salt water until they rise to the surface. Take them out and let them drain. Clean, wash and slice the tomatoes. Pluck the sage leaves from the stalks. Melt butter and fry sage in it.
Grate cheese. Put gnocchi and tomato slices in a flat ovenproof dish. Add sage butter. Sprinkle with cheese and bake in a preheated oven (electric range: 200 °C/ gas: level 3) for 12-15 minutes