Preheat oven to 375°F. Lightly grease a 9×13-inch baking dish and set aside.

Warm olive oil in a medium skillet over medium heat. Add diced onion and cook until translucent, about 5 minutes. Stir in garlic and sage; cook 30 seconds until fragrant.

In a bowl, whisk together pumpkin puree, heavy cream, nutmeg, salt, and pepper. Fold in half the Parmesan. Taste and adjust seasoning—this is your flavor base.

Spread a thin ribbon of pumpkin sauce on the bottom of the dish. Lay 3 noodles side by side. Spoon one-third of the sauce over noodles, dot with ricotta, sprinkle a little mozzarella, then add a handful of spinach if using.

Add another noodle layer, more sauce, ricotta, mozzarella—and finish with the last 3 noodles. Spread remaining sauce on top, then pile on the rest of the mozzarella and Parmesan.

Cover loosely with foil and bake 25 minutes. Remove foil and bake an additional 10–12 minutes until cheese bubbles and edges brown.

Let it rest 10–15 minutes—this helps the layers set and makes slicing neater. Garnish with extra sage leaves or a light drizzle of olive oil.