Preheat Your Oven: First things first, get that oven fired up to 375°F (190°C).
Roast the Squash: In a big bowl, toss those beautiful butternut squash cubes with the olive oil, sage, thyme, ½ teaspoon of salt, and ½ teaspoon of black pepper. Spread them out in a single layer on a baking sheet. Pop them in the oven for about 20-25 minutes, or until they’re fork-tender and smell amazing.
Make the Squash Sauce: Carefully transfer the roasted squash into your blender or food processor. Add the milk, the remaining ½ teaspoon of salt, and the remaining ½ teaspoon of black pepper. Blend it all up until it’s super smooth and creamy. Set this delicious puree aside.
Whip Up the Ricotta Mixture: In a medium bowl, combine the ricotta cheese, 1 cup of your grated mozzarella or Parmesan cheese, the egg, minced garlic, chopped fresh basil, ½ teaspoon of salt, and ½ teaspoon of black pepper. Give it a good mix until everything is well combined.
Start Assembling! Grab your 9×13 inch baking dish. Spread a thin layer of your smooth butternut squash mixture on the very bottom. This prevents the noodles from sticking.
Layer the Noodles: Arrange a layer of lasagna sheets right over the squash mixture.
Add the Ricotta: Spoon about half of your creamy ricotta mixture over the lasagna sheets and spread it out gently.
Sprinkle Some Cheese: Now, sprinkle about a third of the shredded mozzarella cheese over the ricotta.
Repeat the Goodness: We’re going to repeat these layers! Add another layer of the butternut squash mixture, then lasagna sheets, the rest of the ricotta mixture, and another third of the shredded mozzarella cheese.
The Grand Finale Layers: Top with a final layer of lasagna sheets, then spread the remaining butternut squash mixture all over.
Cheese, Glorious Cheese: Finally, sprinkle the last of the shredded mozzarella cheese evenly over the top.
Cover and Bake: Tightly cover your baking dish with aluminum foil. This helps everything steam and cook through nicely. Bake for 25 minutes.
Uncover and Brown: Now, remove the foil. Pop it back in the oven and bake for another 20-25 minutes, or until the top is a beautiful golden brown and the edges are bubbly and irresistible.
Rest is Best: This is the hardest part, but trust me, letting the lasagna rest for about 10 minutes before you slice and serve it makes a world of difference in how well it holds together.