Preheat the oven to 375°F (190°C).

Cook the jumbo shells in a large pot of salted boiling water for 2 minutes less than the package directions for al dente; drain and set aside.

In a large mixing bowl, combine the pumpkin puree, ricotta cheese, 1 cup of the smoked Gouda, the egg, nutmeg, half of the salt, and half of the pepper.

In a medium saucepan over medium heat, melt the butter. Add the sage leaves and cook for 2 minutes until the leaves are crisp and the butter is slightly browned.

Add the minced garlic to the saucepan and cook for 30 seconds until fragrant.

Whisk in the heavy cream and the remaining salt and pepper. Bring to a low simmer and cook for 5 to 7 minutes until the sauce thickens slightly.

Spread 0.5 cup of the sage Alfredo sauce across the bottom of a 9x13 inch baking dish.

Fill each cooked pasta shell with approximately 2 tablespoons of the pumpkin mixture and arrange them in the baking dish.

Pour the remaining Alfredo sauce over the stuffed shells and sprinkle with the remaining 0.5 cup of Gouda and the Parmesan cheese.

Bake for 25 to 30 minutes until the cheese is melted and bubbling and the edges of the shells are golden brown.