Step 1: Prepare the Dough In a saucepan, combine water, milk, butter, sugar, and salt, then bring it to a boil while stirring until the butter melts. Reduce the heat and add flour all at once, stirring vigorously until a smooth ball forms and pulls away from the pan sides, which takes about a minute. Transfer the dough to a mixer bowl and let it cool for 5 minutes. Beat on low speed for 30 seconds to release steam, then add eggs one at a time, beating well after each until the dough becomes smooth, thick, and easy to pipe.

Step 2: Shape and Bake Pipe the dough into 1¾-inch mounds on the prepared baking sheet, spacing them 2 inches apart using a ½-inch round tip. Smooth any peaks with wet fingertips to help them bake evenly. Bake for 22 to 25 minutes without opening the oven door, until they’re golden and well-risen. Once done, crack the oven door and let the puffs sit inside for 30 minutes to dry, then cool them completely on a wire rack.

Step 3: Make the Sauce and Fill For the chocolate sauce, heat heavy cream until steaming, remove from heat, and stir in chopped chocolate and a pinch of salt until smooth. Let it cool slightly. Prepare your filling by scooping ice cream into balls and freezing until firm, or whisk pastry cream until smooth. Assemble by slicing the cooled puffs horizontally, filling them with ice cream balls or piped pastry cream, and drizzling with warm sauce before serving.