Bolognese: 

1. Heat a large 6–7 qt (5.7–6.6L) pot over medium-high heat. Add the Italian sausage and break it into large chunks using a wooden spoon. Sear undisturbed until nicely browned on the bottom, about 2–3 minutes. Continue breaking up the sausage with a wooden spoon, or use a potato masher for faster, more even browning. Cook, stirring occasionally, until browned, crispy, and cooked through, another 3–4 minutes. Transfer the sausage to a bowl or baking sheet, then repeat the process with the ground beef. Once the beef is browned and cooked through, return the sausage to the pot and reduce the heat to medium-low.
2. Add the garlic and stir until fragrant, about 1 minute. Add the tomato paste and stir vigorously to combine. Cook, stirring occasionally, until the tomato paste darkens slightly and begins sticking to the bottom of the pot, about 1–2 minutes. Pour in the crushed tomatoes and water, stirring to incorporate any browned bits from the bottom of the pot. Bring the sauce to a boil, then season with salt and pepper.
3. Reduce the heat to medium-low and let the sauce gently simmer, stirring occasionally, for about 10 minutes, until the flavors come together. Taste and adjust the seasoning as needed.
4. Turn off the heat and stir in all the basil, stems included. Let it steep in the sauce like tea for about 10 minutes while you prepare the béchamel. Remove and discard the basil stems before assembling the lasagna.

‍Béchamel:

1. In a medium-sized pot, melt the butter over medium heat. Whisk in the flour and keep it moving until it looks like pale, wet sand, about 1-2 minutes. Add the white pepper, kosher salt, nutmeg, then whisk to combine.
2. While whisking constantly, gradually stream in the warm milk and cream, adding about one-quarter of the liquid at a time and whisking until smooth after each addition. Continue cooking, scraping the sides and bottom of the pot as necessary, until the sauce thickens enough to coat the back of a spoon, about 5 minutes. Remove from the heat and set aside. If the sauce becomes too thick before assembly, whisk in a small splash of warm milk to loosen it.
   

Assembly:

1. Preheat the oven to 350°F (177°C). Bring a large pot of heavily salted water to a boil. Add the lasagna noodles and cook until pliable but still quite firm, about 2–3 minutes. Drain and lay the noodles flat on lightly oiled baking sheets or parchment paper to prevent sticking.
2. In a large bowl, combine the skim milk mozzarella, whole milk mozzarella, and Parmigiano-Reggiano. Toss by hand until the cheeses are evenly distributed.
3. In a deep 13 × 9-inch (33 × 23cm) baking dish, spread about 1½ cups of Bolognese evenly across the bottom. Arrange a layer of lasagna noodles over the sauce, slightly overlapping them as needed. Spread approximately ¾ cup of béchamel over the noodles, followed by an even layer of the cheese mixture. Repeat the layers, distributing the Bolognese, noodles, béchamel, and cheese evenly throughout the dish. Aim for five layers of noodles, adjusting the quantities as needed to use all the sauce and cheese. Finish with a generous layer of cheese on top.
4. Lightly cover the baking dish with aluminum foil, tenting it slightly so the foil does not touch the cheese. Transfer to the preheated oven and bake for 20 minutes. Remove the foil, increase the oven temperature to 400°F (204°C), and continue baking until the edges are bubbling and the top is golden brown, about 25–30 minutes.
5. Remove the lasagna from the oven and let it rest at room temperature for at least 15 minutes. This step is essential for clean slices. Garnish with additional finely grated Parmigiano-Reggiano, followed by the chopped parsley and basil. Slice, serve, and enjoy!