Cook broth, shallots, and garlic in medium saucepan over medium heat, stirring occasionally, until shallots are tender and liquid has reduced by half.
Stir in alfredo sauce, pumpkin, sage, salt, and pepper.
Cook, stirring occasionally, until heated through.
Pour sauce into baking pan; arrange stuffed shells on top.
Bake, covered, at 350 degrees for 15 minutes.
Uncover and bake for an additional 10-15 minutes. Sprinkle with extra mozzarella or parmesan cheese, if desired.
(*Sauce recipe adapted from Buitoni)