Preheat the oven to 350 degrees and grease a large cast iron skillet.
Boil the pasta according to the package instructions. Drain and set aside.
In the skillet, melt the butter and add the flour. Whisk together over medium heat for a few minutes.
Gradually add the milk to the butter and flour. Whisk for about 5 minutes over medium heat until it starts to thicken.
Remove the pan from the stove and stir in the cheddar cheese, pumpkin puree, and salt. Add the cooked pasta and stir to coat evenly. Sprinkle with the grated Parmesan.
Cover the skillet with foil and bake for 20 minutes. Remove the foil and bake for about 10 more minutes, until the top begins to brown.