Warm the olive oil in a wide skillet, and add the chopped onion and garlic. Cook over medium-high heat until softened, then add the salt & pepper, and sage. Stir, add the wine, raise the heat and boil off most of the liquid. Add the tomatoes and tomato paste, stir, and simmer until thickened, about 15 minutes.
Put the ricotta, 1 1/2 cups mozzarella, and parmesan in a bowl. Grate in the nutmeg, and mix with a fork.
Bring a large (6 quart) pot of water to a boil, and salt it fairly heavily. Boil the lasgana sheets for about 3 minutes, just till they float, then drain, rinse with cold water, and drape over the colander and pot edges to drain.
Spread half the sauce in the bottom of a 13 x 9 x 2 baking dish, and make a single layer of noodles on top, squeegeeing the water off with your fingers. Layer half the ricotta mixture over the noodles - you'll have to drop little bits here and there over the noodles, and flatten them out. Put another layer of noodles on top of the cheese filling, make another layer using the last of the cheese, top with the last of the noddles, and then top them with the last of the sauce.Bake at 375° for about 20 minutes, then top with the remaining mozzarella, and bake another 10 minutes. Let rest for about 10 minutes before serving, to firm up.