Place the water, salt and butter in a 2-quart saucepan and bring to a boil. Have a whisk and a wooden spoon ready. Remove the pan from the heat and dump the flour in all at once, whisking it together. Return the pan to the burner and start stirring with spoon. Cook for 3 minutes, stirring constantly, until the dough starts to pull easily from the sides of the pan and form a ball. Remove from the heat and stir until tepid, 6-8 minutes. Add the eggs, one at a time, stirring in each one completely before adding the next. Pour the resulting mixture into a mixing bowl and cover with plastic wrap, using your fingers to lay the plastic wrap so that it rests directly on the top of the batter. Set aside at room temperature.