Preheat your oven to 400°F (200°C).

Bring salted water to a boil and cook the jumbo pasta shells until al dente, about 8-10 minutes, then drain and rinse.

Sauté diced yellow onion and half of the chopped sage in olive oil over medium heat for 4-5 minutes.

Combine ricotta, pumpkin puree, 1/3 cup of gouda, minced garlic, nutmeg, salt, and pepper in a mixing bowl. Fold in sautéed onions.

Melt butter in a saucepan. Brown it slightly, add remaining sage, whisk in flour, then gradually add heavy cream, season with salt and pepper.

Spread half of the Alfredo sauce in a baking dish. Fill shells with pumpkin filling and arrange them in the dish.

Pour remaining Alfredo sauce over the shells and sprinkle with gouda cheese.

Bake in the preheated oven for 20-25 minutes until cheese is bubbly and golden.

Let cool for a few minutes, garnish with black pepper and fried sage leaves, then serve.