Bring a large pot of salted water to a rolling boil. Add the jumbo pasta shells and cook until al dente, usually about 10–12 minutes. Drain and cool slightly.

In a mixing bowl, combine the pumpkin puree, gouda cheese, ricotta cheese, garlic powder, salt, and pepper. Blend until smooth and creamy.

Fill each cooked shell with about two tablespoons of the pumpkin and gouda filling and place in a greased baking dish.

In a medium saucepan, melt the butter over medium heat until light golden brown. Whisk in the heavy cream and add sage leaves; simmer until thickened.

Pour half of the alfredo sauce over the stuffed shells and sprinkle with grated parmesan cheese.

Preheat the oven to 350°F (175°C). Cover with foil and bake for 25 minutes. Remove foil and bake for an additional 10 minutes.

Let cool slightly, then drizzle with remaining alfredo sauce before serving.