Preheat your oven to 400°F (200°C) and bring a large pot of salted water to a boil. Cook the jumbo pasta shells until al dente, about 9-11 minutes, then drain.

In a skillet, heat a tablespoon of olive oil over medium heat. Add diced yellow onion and half of the chopped sage, sautéing for about 5 minutes.

In a large mixing bowl, combine ricotta, pumpkin puree, one portion of gouda, and minced garlic. Stir in the sautéed onions and season with salt, pepper, and nutmeg.

In a saucepan, melt 4 tablespoons of butter over medium-high heat until browned. Add remaining sage and sauté for 30 seconds. Whisk in flour and gradually add half of the heavy cream.

Spread half of the alfredo sauce in a baking dish. Fill each cooked shell with the ricotta mixture and arrange them in the dish.

Pour remaining alfredo sauce over the shells and sprinkle with gouda. Cover with foil and bake for 20-25 minutes.

Remove from oven and let cool for a few minutes. Garnish with fried sage leaves and serve.