Bring a large pot of salted water to a boil.

Add the pasta and cook until al dente according to package directions.

Meanwhile, set a large skillet over medium heat and melt the butter.

Add diced onion and optional red pepper flakes, then cook 5–7 minutes until soft and translucent.

Add minced garlic and cook 1 minute, stirring to prevent burning.

Stir in pumpkin puree and sauté 1 minute to deepen flavor.

Pour in heavy whipping cream and whisk until smooth.

Season with salt, pepper, sage, nutmeg, and brown sugar.

Reduce heat and simmer 2–3 minutes until sauce thickens.

Stir in parmesan cheese until melted and sauce becomes creamy.

Drain cooked pasta, reserving a splash of pasta water.

Add pasta to skillet and toss to coat evenly in sauce.

Loosen with reserved pasta water if needed.

Serve topped with extra parmesan and black pepper.