Boil the noodles. To cook the lasagna noodles, bring a large pot of salted water to a rolling boil. Add 5-6 lasagna noodles at a time and cook them until al dente, in the case of the brand I used I boiled them for about 4 minutes. Store them on a baking sheet between layers of parchment that have been drizzled with olive oil.
Make the bechamel. In a non-reactive 2 qt saucepan, melt the butter over medium heat. Once the butter is hot and foamy, sprinkle in the flour and whisk well to combine. Cook for 2-3 minutes, whisking constantly. Whisk in the warm milk 1 cup at a time, whisking constantly until all the milk is added. Bring to a simmer until thick and stir in 1/2 cup of parmesan, salt and freshly cracked pepper to taste plus the nutmeg. Cool for 10 minutes.
Assemble the lasagna. Lightly grease a deep 9x13 baking dish (see notes below). Spread a thin layer of bechamel. Use 4 noodles and lay them on top of the bechamel. Spread 1 1/2 cups bolognese sauce over the noodles. Drizzle 3/4 cup of bechamel over the bolognese. Sprinkle with some of the diced mozzarella and 1/2 cup of the parmesan. Repeat with the remaining ingredients. On the top layer, just spread the bechamel with mozzarella and parmesan. At this point, you can cover and refrigerate the unbaked lasagna overnight.
Preheat an oven to 375ºF.
Bake. Cover the lasagna with foil and bake for 1 hour, covered. Remove the cover and bake for 15 minutes, until the top is browned and bubbly. Rest the lasagna for 20-30 minutes before serving. Top with freshly grated parmesan.