Bring water to a boil in a small Dutch oven. Combine cornmeal, baking powder, sugar, salt, and onion; slowly add to boiling water, stirring constantly until mixture is smooth. Remove from heat; add butter, stirring until melted. Cool mixture 10 minutes.
Shape batter into 2- x 1-inch oblong rolls. Deep fry in hot oil (375°), cooking only a few at a time. Fry until hush puppies are golden brown. Drain well on paper towels. Serve hot.