In a saucepan over medium heat, melt the butter. Add the minced garlic and chopped sage, cooking for about 1.0-2.0 minutes until fragrant. Pour in the heavy cream and bring it to a gentle simmer. Season with salt and pepper. Let simmer for about 5.0-7.0 minutes until it thickens slightly. Stir occasionally, then remove from heat.
In a skillet, heat a tablespoon of olive oil over medium heat. Add the chopped onion and cook until translucent (about 3.0-4.0 minutes). Stir in the minced garlic and fresh spinach, cooking until the spinach wilts. Season with salt, pepper, nutmeg, and cinnamon. Set aside.
In a large bowl, mix the pumpkin puree, ricotta cheese, and half of the Parmesan cheese. Season with salt and pepper, mixing until well combined.
Preheat the oven to 350.0.
In a greased baking dish, spread a thin layer of the sage cream sauce at the bottom. Place three lasagna noodles on top. Spread half of the pumpkin mixture over the noodles, followed by half of the sautéed spinach and onion mixture, then sprinkle a third of the mozzarella cheese. Repeat the layering process: noodles, remaining pumpkin mixture, remaining spinach, and another third of mozzarella. Top with the last three lasagna noodles and finish with the remaining mozzarella and Parmesan cheese.
Pour the remaining sage cream sauce over the top of the assembled lasagna. Cover the dish with aluminum foil and bake for 25.0 minutes. Remove the foil and bake for an additional 15.0-20.0 minutes until the cheese is bubbly and golden.
Let the lasagna sit for 10.0 minutes before slicing. Serve with additional sage cream drizzled on top if desired, and enjoy!
Notes
Can be made ahead and stored in the refrigerator before baking.