Bring a large pot of salted water to a boil and cook the pasta until just al dente, about 8 minutes. Drain and set aside.
In a large skillet, melt the butter over medium heat and add the diced onion. Sauté until translucent and fragrant, about 5 minutes, until it begins to soften and smell sweet.
Stir in the pumpkin puree, cinnamon, nutmeg, and heavy cream. Let the mixture simmer gently, stirring occasionally, until warmed through and slightly thickened, about 3 minutes.
Add the shredded cheddar cheese to the pumpkin sauce, stirring until melted and smooth. Taste and adjust seasoning if needed.
Combine the cooked pasta with the pumpkin cheese sauce, tossing gently until evenly coated.
Preheat your oven to 180°C (350°F). Butter a baking dish and transfer the coated pasta into it, spreading evenly.
Mix breadcrumbs with olive oil, then sprinkle evenly over the top of the pasta.
Bake uncovered for 20-25 minutes until bubbling around the edges and the breadcrumbs are golden brown.
Remove from the oven and let sit for a few minutes. Serve hot, with a crispy topping and a creamy, cheesy interior that’s perfect for cozy fall nights.