01 - Preheat oven to 400°F. Toss diced butternut squash with 1 tablespoon olive oil, salt, and pepper. Spread evenly on a baking sheet and roast for 20-25 minutes until tender and lightly caramelized. Reduce oven temperature to 350°F.
02 - While squash roasts, heat remaining olive oil in a large skillet over medium heat. Add onions and cook until translucent, about 3-4 minutes. Add garlic and cook for another 30 seconds until fragrant.
03 - Add sausage to the skillet. Cook, breaking up with a spoon, until browned and cooked through. Stir in dried oregano, dried sage, and a pinch of nutmeg. Remove from heat.
04 - Transfer roasted butternut squash to a bowl and mash lightly with a fork, leaving some chunks for texture.
05 - In a separate bowl, combine ricotta with egg, half the Parmesan, salt, and pepper until smooth.
06 - Lightly oil a 9x13-inch baking dish. Spread 1/2 cup tomato sauce on the bottom. Layer 3-4 noodles over the sauce. Spread one-third of the ricotta mixture, one-third of the sausage, one-third of the squash, a handful of mozzarella, and about 1/3 cup sauce.
07 - Repeat layers twice more: noodles, ricotta, sausage, squash, mozzarella, sauce. Finish with final noodle layer, remaining sauce on top, and remaining mozzarella and Parmesan.
08 - Cover with foil (sprayed with oil to prevent sticking). Bake at 350°F for 30 minutes. Remove foil and bake 15-20 minutes until cheese is golden and bubbling.
09 - Let lasagna cool for 10-15 minutes before slicing. Garnish with fresh basil if desired.