1. Fit a large soup kettle with a steamer basket; fill kettle with enough water to come to the bottom of the basket. Bring water to boil; add squash. Cover, and cook over medium-high heat until squash is very tender when pierced with a thin-bladed knife, 14 to 16 minutes.
2. Transfer squash to a shallow bowl, add butter, ginger, and salt and pepper to taste; mash with a fork to a coarse puree. Adjust seasoning and serve. Can be covered and refrigerated overnight; reheat in microwave or double boiler.