Puree squash in food processor, blender, or mash by hand. Return to saucepan and stir in remaining ingredients. Blend well. Turn into an ovenproof serving dish. Dish may be prepared up to a day ahead and refrigerated (covered tightly with plastic wrap) or baked immediately for serving.

Bake in 325°F oven for about 20 minutes (if the squash is still hot, or if prepared in advance and squash is cold, bake for 30 minutes. Serve with a tablespoon of butter, if desired.