Bring a large pot of water to a boil. Once boiling, generously season the water with salt. Add the fusilli (or pasta of choice) & cook, stirring occasionally to prevent sticking, to al dente. (Al dente cooking time is typically noted on package directions.) Once the pasta reaches al dente, carefully dip a liquid measuring cup into the pot, reserving about 1 cup of starchy pasta water, & set aside. Drain the pasta – but do not rinse – & set aside.
Meanwhile, as the water comes to a boil, begin building the pumpkin vodka sauce. Add the olive oil to a large skillet over medium heat. Once the oil is hot & shimmering, stir in the shallot. Season with ½ teaspoon kosher salt & ground black pepper as desired. Cook, stirring occasionally, until softened & fragrant, 3-4 minutes. Stir in the sage, garlic, & crushed red pepper flakes (if using) & cook 1-2 minutes longer, until fragrant.
Reduce the heat under the skillet to medium-low. Add tomato paste & pumpkin to the skillet, stirring to coat the softened aromatics. Cook 10-12 minutes, stirring occasionally, until the mixture darkens a little & begins to coat the bottom of the skillet. Deglaze the skillet by slowly pouring in the vodka while constantly stirring & scraping up any browned bits that may have formed on the bottom of the skillet. Once vodka is almost completely cooked off, stir in the heavy cream, grated parmesan, & nutmeg. Taste & adjust seasonings as needed. Reduce heat to maintain a gentle simmer.
Add the cooked pasta to the pumpkin vodka sauce. Toss to combine well – the sauce should evenly coat the pasta. Add in some of the reserved pasta water if the sauce needs to loosen up a little; add in an extra handful of parmesan if it needs to tighten up more. Cook 1-2 minutes longer, allowing the pasta to meld together with the pumpkin vodka sauce. Remove from the heat.