Combine water and butter in a medium saucepan; bring to a boil. Add salt and flour, all at once, stirring vigorously over low heat until mixture leaves sides of pan and forms a smooth ball. Remove from heat, and cool slightly.
Add eggs, one at a time, beating well after each addition; beat until batter is smooth.
Drop batter by rounded teaspoonfuls, 3 inches apart, onto greased baking sheets. Bake at 425° for 15 minutes or until puffed and golden brown. Remove to wire racks, and cool away from drafts.
Cut tops off cream puffs; pull out and discard soft dough inside. Fill bottom halves with filling; replace top, and spread frosting on top half. Serve immediately or refrigerate.