In a large saucepan over medium heat, melt the butter.
Add garlic and onion, cooking for 4-5 minutes, or until they begin to soften and brown.
Add heavy cream, milk, 6 oz. goat cheese, 1 cup Parmesan cheese, pumpkin, and pepper.
Reduce heat to low, and cook, stirring constantly, until sauce thickens, about 5 minutes.
Stir in sage, and remove from heat.
Add pasta to sauce, stirring to coat.
Pour mixture into a lightly greased 13x9-inch baking dish.
Sprinkle with bacon, remaining goat cheese, and remaining Parmesan.
Cover casserole with foil.
Bake at 350 degrees for 20 minutes.
Remove foil, and bake an additional 5-10 minutes, or until cheeses are melted, and the edges are golden.
Garnish with scallions, and serve hot.