Cook the jumbo pasta shells in salted boiling water until al dente, about 9–10 minutes. Drain, rinse under cold water, and set aside to cool slightly.

In a skillet, heat olive oil over medium heat and sauté diced onion with half the chopped sage for 4–5 minutes, until soft and fragrant.

In a bowl, mix ricotta, pumpkin puree, ⅓ cup shredded Gouda, minced garlic, nutmeg, salt, and pepper. Stir in the sautéed onions and sage until smooth and creamy. If too thick, add a tablespoon of cream.

Melt butter in a saucepan over medium-high heat until golden and nutty. Lower heat, add the remaining sage, and whisk in flour. Gradually pour in half the cream, whisking until thickened, then add the rest. Season with salt and pepper and simmer until the sauce coats the spoon.

Preheat oven to 400°F (200°C). Spread half the Alfredo sauce on the bottom of a baking dish. Fill each shell with about 2 tablespoons of the pumpkin mixture and arrange them in the dish. Pour the remaining sauce over the top and sprinkle with the rest of the Gouda.

Bake for 20–25 minutes, until bubbling and lightly golden.

Fry a few sage leaves in butter until crisp, then scatter them over the baked shells. Finish with cracked black pepper and serve warm with salad or roasted vegetables.