Preheat over to 350°F, and coat a 2 quart casserole dish with cooking spray or oil.
While preparing the sauce, cook the pasta to al dente according to package directions, drain, and set aside.
To prepare the sauce, melt butter in a large, shallow saucepan over medium heat, and add the garlic and sage. Cook for a couple minutes to allow the flavors and aromas to release.
Add the half and half, chicken broth, pumpkin, and nutmeg. Over medium-low heat, bring to a summer and cook several minutes until thickened slightly.
Stir in 1/2 cup parmesan cheese, salt, and pepper. Remove from the heat.
Add pasta, peas, and sausage to the sauce and stir to coat completely.
Transfer the pasta to the prepared casserole dish, and sprinkle with remaining 1/4 cup parmesan cheese.
Bake in the preheated oven for 20-25 minutes, or until heated through, and lightly browned on the top.