Heat the oven to 425°. In a medium saucepan, bring milk, butter, salt, and 1⁄2 cup water to a boil over high heat. Add flour; stir until a dough forms. Reduce the heat to medium and cook, stirring constantly with a wooden spoon, until slightly dried, about 2 minutes. Transfer the dough to a bowl and, using a hand mixer, beat in eggs, one at a time, until smooth.