1 1/3 cups ricotta cheese, well drained
1 cup packed cooked spinach, well squeezed and chopped
1/4 cup diced Fontina cheese
1/4 cup diced Swiss cheese
1/4 cup grated Parmigiano-Reggiano cheese
1/4 cup plus 2 tablespoons toasted fresh bread crumbs
2 tablespoons (1/4 stick) butter, softened
2 large egg yolks, beaten
Salt to taste
1 teaspoon freshly grated nutmeg
1 1/2 cups tomato sauce

In a large bowl, mix all the ingredients except the tomato sauce.

Preheat the oven to 350ºF.

Using 2 soup spoons, form gnocchi into oval or egg shapes using a little less than 1/4 cup of the mixture for each. There should be about twenty 2 1/2-inch-long gnocchi. Place them close together, but not touching, in a buttered 13 1/2 by 8-inch baking dish. Cover the gnocchi with the tomato sauce and bake for 20 to 25 minutes or until hot. Serve immediately.

Note: Sometimes a white sauce is used in addition to the tomato sauce. Spread the baking dish with the white sauce before adding the gnocchi.