Begin making the filling by heating the oil, adding the onion, and cooking until translucent.
Add garlic, and cook for about 30 seconds without burning. Add ground beef and sausage, breaking up any clumps as the meat cooks.
Add salt and pepper, and stir well. Add nutmeg, and mix in. When the meat is cooked but not dry, add tomatoes and basil. Lower the heat to simmer for about 30 minutes.
Add sugar to cut the acid and some wine to taste. Let the filling cool completely, and put it in the refrigerator overnight.
To assemble the lasagna, preheat the oven to 375°.
Add beaten egg to the ricotta and a little sauce, and stir until completely incorporated. Spread a thin layer of filling over the bottom of an oiled pan. Add a layer of lasagna sheets over the filling, cutting the sheets as necessary to cover the bottom of the pan.
Then, cover the sheets with more filling, ricotta mixture, shredded mozzarella, and grated Italian cheese.
Repeat, making as many layers as your pan will hold, ending with filling, shredded mozzarella, and grated cheese - in that order.
Bake for about 45 minutes or until bubbly. If your oven runs hot, and it looks like it might burn, gently put a piece of foil over the top.
Remove from oven, and let stand for 20-30 minutes before serving.