In a well-buttered, 9-by-13-inch ceramic baking dish, arrange 3 lasagna noodles in different directions in the dish, leaving about 2 inches of overhang. Spoon a scant 1/4 cup of the tomato sauce over each lasagna noodle and sprinkle with a little grated Parmigiano-Reggiano cheese. Set a piece of mozzarella and Fontina on each lasagna noodle and add a few chunks of sausage. Fold the overhanging lasagna noodles on top of the cheese and sausage. Repeat the process with the remaining lasagna noodles, tomato sauce, mozzarella, Fontina and sausage, sprinkling with a little more Parmigiano-Reggiano cheese. Brush the softened butter on any bare pasta and curly edges and sprinkle with Parmigiano-Reggiano.