Peel the squash, cut in half, and scrape out seeds. Cut into large dice.
Place in perforated steamer pan. Steam until tender. (Alternative pan‐steaming method: Place in heavy pot. Add 1 in. [2.5 cm] water, cover, and cook slowly until tender. Drain well.)
Purée the squash with a food mill. Add the butter, sugar, and seasonings. Whip until light