Preheat your oven to 400°F (200°C) and grease the baking dish.

Bring a large pot of salted water to a boil and cook the jumbo pasta shells until al dente, about 9-11 minutes. Drain and rinse under cold water.

In a skillet, heat olive oil and sauté diced yellow onions with half of the sage for about 4-5 minutes until translucent.

In a mixing bowl, combine ricotta, pumpkin, gouda, garlic, nutmeg, salt, pepper, and the sautéed onions and sage. Mix until creamy.

In a saucepan, melt butter over medium-high heat until golden brown and foamy. Add remaining sage leaves for flavor.

Whisk in the flour, then gradually add half of the heavy cream, stirring until thickened. Add remaining cream and season with salt and pepper.

Spread half of the alfredo sauce in the greased baking dish. Fill each pasta shell with about 2 tablespoons of the pumpkin filling and place them seam-side up in the dish.

Pour the remaining alfredo sauce over the filled shells and sprinkle with leftover gouda.

Bake in the preheated oven for 20-25 minutes until bubbly and golden brown. Watch closely towards the end.

Let rest for a few minutes before serving, garnished with fried sage leaves.