For the Butternut Squash Filling:
1 large butternut squash (peeled, seeded, and cubed)
2 tablespoons olive oil
1 teaspoon salt
1/2 teaspoon black pepper
1/4 teaspoon ground nutmeg
1 tablespoon fresh sage (chopped, or 1 teaspoon dried sage)

For the Ricotta Mixture:
2 cups ricotta cheese
1/2 cup grated Parmesan cheese
1 egg
1 teaspoon fresh thyme (chopped, or 1/2 teaspoon dried thyme)
Salt and pepper (to taste)

For the White Sauce (Béchamel):
4 tablespoons butter
4 tablespoons all-purpose flour
3 cups milk (whole or 2%)
1/4 teaspoon ground nutmeg
Salt and pepper (to taste)

For Assembly:
12 lasagna noodles (cooked according to package instructions)
2 cups shredded mozzarella cheese
Fresh sage leaves for garnish (optional)