In a saucepan, bring the water, sugar, salt, and oil to a boil.
Add the flour all at once and stir vigorously until a thick dough forms and pulls away from the sides of the pan.
Transfer the dough to a mixing bowl. Beat in the eggs one at a time until the dough is smooth, glossy, and pipeable.
Transfer the dough to a piping bag fitted with a round tip. Line a cookie sheet with parchment paper.
Pipe small mounds of dough onto the parchment, spacing them apart.
Beat the remaining egg and brush a thin layer over the tops of the piped dough.
Bake until the puffs are fully risen and deeply golden.
Cool, then dust with powdered sugar before serving.
