In a saucepan over medium heat, combine butter, sugar, water, milk, salt, and vanilla. Stir until butter melts and the mix boils.
Swiftly add the flour, stirring constantly, until the mixture forms a smooth ball and detaches from the pan's sides.
Transfer to a mixer fitted with a paddle. Mix on medium until the dough cools (about 5 minutes).
Beat in the eggs gradually, ensuring a smooth, shiny mix. Remember to scrape the bowl sides.
Transfer the dough to a piping bag with your chosen tip. Refrigerate overnight.
Preheat the oven to 190°C (375°F). Prep a baking sheet with a perforated mat or parchment.
Pipe dough onto the sheet, spacing each portion. Optionally, top with craquelin.
Bake at 190°C for 35 minutes. Avoid opening the oven. Then reduce to 170°C (340°F), baking for an additional 15 minutes or until golden.
Post-baking, pierce each pastry to release steam. Allow them to cool before filling or decorating.