Preheat your oven to 400°F (200°C). Toss the cubed squash with olive oil, salt, and pepper, and spread evenly on a baking sheet. Roast for about 25-30 minutes, stirring halfway through, until tender and slightly caramelized. This is the secret to developing deep, sweet flavors that make holiday dishes food like this so memorable.

While the squash is roasting, melt the butter in a saucepan over medium heat. Whisk in the flour and cook for about 1-2 minutes until golden. Gradually add the warmed milk, whisking constantly to prevent lumps. Season with nutmeg, salt, and pepper. Simmer until thickened, about 5-7 minutes.

In a mixing bowl, combine the ricotta cheese with one egg and a pinch of salt. This helps to create a creamy, luscious layer that binds the lasagna beautifully.

Spread a thin layer of bechamel sauce on the bottom of your baking dish. Layer with three lasagna noodles. Top with half of the roasted butternut squash, half of the ricotta mixture, a sprinkle of chopped sage, and a handful of mozzarella. Repeat the layers, finishing with a final layer of noodles, bechamel, mozzarella, and Parmesan cheese. Decorate the top with a few whole sage leaves.

Cover the dish with foil and bake at 375°F (190°C) for 30 minutes. Remove the foil and bake another 15 minutes, or until golden and bubbly. Let it rest for at least 10 minutes before slicing.