01 - Preheat oven to 400°F. Line a baking sheet and set aside.
02 - Toss diced beets with 1 tablespoon olive oil, maple syrup, balsamic vinegar, and a pinch of salt and black pepper. Spread evenly on baking sheet and roast for 25 to 30 minutes, turning halfway, until beets are tender and caramelized.
03 - Bring a large pot of salted water to a boil. Add pasta and cook until just al dente according to package directions. Reserve 1/2 cup pasta cooking water, then drain the pasta.
04 - Heat a large skillet over medium heat. Melt butter with remaining 1 tablespoon olive oil. Add chopped onion and sauté for 3 minutes until translucent, then stir in minced garlic and cook 1 minute longer.
05 - In skillet, add pumpkin puree, heavy cream, nutmeg, chili flakes, salt, and pepper. Simmer gently for 3 to 4 minutes, thinning with reserved pasta water for a silky consistency if needed.
06 - Add drained pasta to the skillet, tossing to evenly coat with pumpkin sauce. Incorporate grated Parmesan and spinach (if using), stirring until cheese melts and spinach wilts.
07 - Divide warm pasta among serving plates. Garnish with roasted maple beets and additional Parmesan cheese. Serve promptly.