Preheat your oven to 375°F.

Cook the jumbo pasta shells according to package instructions until al dente. Drain and set aside to cool slightly.

In a mixing bowl, combine the pumpkin puree, Gouda cheese, ricotta cheese, Parmesan cheese, garlic powder, salt, black pepper, and nutmeg. Mix until well combined.

Stuff each cooked pasta shell with the pumpkin and cheese mixture, using a spoon or a piping bag for easier filling.

In a skillet, heat the olive oil over medium heat. Place the stuffed shells in the skillet and cook for about 5 minutes, turning gently until they are lightly golden. Transfer the shells to a greased baking dish.

In the same skillet, melt the unsalted butter over medium heat. Continue cooking until the butter turns golden brown and smells nutty, about 5-7 minutes.

Add the heavy cream, Parmesan cheese, dried sage, salt, and pepper. Stir until the sauce is smooth and heated through.

Pour the brown butter and sage Alfredo sauce over the stuffed shells in the baking dish.

Bake in the preheated oven for 20-25 minutes, until the sauce is bubbly and the shells are heated through.

Let the dish cool for a few minutes before serving. Garnish with additional sage or Parmesan if desired.