Add the water, milk, and butter to a saucepan and bring to a boil. As soon as it starts boiling, remove it from the heat.
Stir in the sifted flour and salt using a whisk. Return the pan to low heat and cook the mixture for a few minutes until it forms a smooth, dry dough ball that pulls away from the sides of the pan. The bottom may lightly brown, just keep stirring with a spatula.
Remove from heat and transfer the dough to a mixing bowl. Add the eggs one at a time, stirring continuously with a spatula. Work fairly quickly so the eggs don’t start to cook.
If mixing by hand feels too heavy, you can use a hand mixer on low speed. The final dough should be smooth and glossy.
Transfer the dough to a sturdy piping bag fitted with a plain tip. Pipe small mounds onto a baking sheet lined with parchment paper. If peaks form on top, lightly press them down with a damp finger.
Bake in a preheated oven at 400°F/200°C (conventional oven) for 15-20 minutes, or until golden brown and cooked through.