Preheat your oven to 375°F (190°C) and grease a 9x13-inch baking dish with olive oil or butter.

Bring a large pot of salted water to a boil, then add the pasta shells. Cook according to package instructions until al dente, about 10-12 minutes, then drain and rinse under cold water.

In a large mixing bowl, combine pumpkin puree, shredded Gouda, ricotta, grated Parmesan, garlic powder, nutmeg, chopped sage, olive oil, and a pinch of salt and pepper. Mix until creamy.

Spoon a generous amount of filling into each cooled pasta shell and place them seam side up in the greased baking dish.

In a medium saucepan, melt the unsalted butter over medium heat until golden brown and nutty, about 4-5 minutes. Add the heavy cream and remaining sage, stirring to combine.

Pour the brown butter sage Alfredo sauce evenly over the stuffed shells, smoothing it out to ensure coverage.

Cover with foil and bake for 20 minutes. Remove the foil and bake for an additional 10-15 minutes until cheese is melted and bubbly.