Begin by bringing a large pot of salted water to a rolling boil over high heat. Once boiling, carefully add the jumbo pasta shells and cook for approximately 10-12 minutes until al dente. Drain the shells in a colander and rinse them briefly with cold water to stop the cooking process. Set aside to cool.

In a mixing bowl, combine the canned pumpkin puree, ricotta cheese, and smoked Gouda cheese. Season generously with salt, pepper, and a handful of chopped fresh sage. Mix well until the filling is smooth and creamy.

Take each cooled jumbo shell and gently fill it with the pumpkin and Gouda mixture using a teaspoon or a piping bag. Place each stuffed shell seam-side up into a greased baking dish.

In a medium saucepan over medium heat, melt the unsalted butter, stirring frequently until it turns golden brown and develops a nutty aroma. Once browned, reduce the heat and slowly add the heavy cream, whisking together with grated Parmesan, salt, and pepper until the sauce is smooth and creamy.

Pour half of the warm brown butter Alfredo sauce over the stuffed shells, reserving the other half for later. Sprinkle additional shredded Gouda on top.

Preheat your oven to 350°F (175°C). Once ready, place the baking dish in the oven and bake uncovered for 25-30 minutes, or until the edges of the shells are bubbly and slightly golden. Drizzle with the reserved brown butter Alfredo sauce before serving.