I start by filling a large stockpot with water and salting it generously. This is my one chance to season the pasta itself. Bring it to a rolling boil before moving on to the sausage. Having this going first means everything finishes around the same time.
While the water heats, I cook the Italian sausage and shallot in a large nonstick pan over medium-high heat. I break the sausage apart with a wooden spoon as it browns. Once it's cooked through, I stir in the garlic, sage, and red pepper flakes for a couple of minutes.
Once the water is boiling, I add the pasta and cook it until just al dente, not mushy. Before draining, I always scoop out about 2 cups of that starchy pasta water. It's key for a silky sauce later. Then I drain the rest.
Back in the sausage pan, I pour in the white wine and scrape up all those flavorful browned bits from the bottom. Then I stir in the pumpkin purée, heavy cream, and chopped kale, letting the kale wilt slightly before turning off the heat.
I combine the drained pasta and sauce in the big stockpot, along with about 3/4 cup of the reserved pasta water. I toss it well, adding more starchy water a little at a time until the sauce turns smooth and glossy, then taste and adjust the seasoning.
Finally, I plate the pasta warm and finish it with a generous shower of freshly-grated Parmesan and a crack of black pepper. This last step really makes the dish feel finished and restaurant-worthy.