Preheat your oven to 400°F (200°C) and gather a 9x13-inch baking dish.

Cook the jumbo pasta shells in a large pot of salted boiling water until al dente, about 9-11 minutes. Drain and let cool.

In a skillet over medium heat, sauté diced yellow onion and half of the chopped sage in olive oil for about 5-7 minutes until translucent.

In a mixing bowl, combine ricotta cheese, pumpkin puree, gouda, minced garlic, nutmeg, salt, and pepper until creamy. Fold in the sautéed onion mixture.

Melt butter in a saucepan over medium heat until bubbling and light brown. Add the remaining chopped sage and cook for 2 minutes.

Whisk in the flour until smooth, then gradually add heavy cream, stirring until thickened, about 3-5 minutes.

Spread half of the Alfredo sauce in the bottom of the baking dish. Stuff each shell with about 2 tablespoons of the filling and arrange them in the dish.

Pour the remaining Alfredo sauce over the filled shells and sprinkle with remaining gouda. Bake for 20-25 minutes until bubbly and golden.

Let cool for a few minutes, then garnish with freshly cracked pepper and fried sage leaves. Serve warm.