eclair recipe

1 cup water - 1/2 cup unsalted butter - 1/4 teaspoon salt - 1 cup all-purpose flour - 4 large eggs **For the Pastry Cream:** - 2 cups whole milk - 1/2 cup granulated sugar - 1/4 cup cornstarch - 1/4 teaspoon salt - 4 large egg yolks - 2 tablespoons unsalted butter - 2 teaspoons vanilla extract