Cook potatoes whole in salted water, peel and Strain. Puree is kneaded with egg. Gradually add flour and Parmesan and stir until a smooth homogeneous dough. It forms a thin roll - as skinless sausage, add some flour and cut into pieces 2-3 cm long. Each piece is pressed with a fork to obtain cross notches. During this time in a pan pour 2 liters of water, put it 1 tsp salt and boil. Gnocchi carefully placed in the water and cook until emerge. Topping is prepared by grated onion fry until golden. Add water and stew for another 2-3 minutes. Add the peeled and chopped tomatoes, add salt and seasoned with black pepper. Stews further 10 minutes. Optional can add a little basil. And finally add the cream and allow to boil. Gnocchi are placed in a fireproof container and covered with topping. Top covered with cheese cut into strips (or grated) and bake in a preheated oven for 10 minutes. Serve warm.