Combine cornmeal, baking powder, and salt; stir well. Add chopped onion and egg, mixing well. Slowly add milk, stirring just until dry ingredients are moistened.
Carefully drop batter by tablespoonfuls into deep, hot oil (375°), cooking only a few at a time. Fry about 2 minutes; turn and fry an additional 2 minutes or until hush puppies are golden brown. Drain well on paper towels.