Preheat oven to 400°F (204°C).
In a pot on medium heat, add milk, water, butter, and salt and stir together. Bring to a boil. Once it boils, remove from heat and sift in the flour to mix quickly to create the batter.
After the flour is mixed in, lightly cook the dough on medium-low heat while mixing continuously. After about 1-2 minutes and a thin layer forms on the bottom of the pot, transfer the dough into a mixing bowl. Allow to cool down for a few minutes before adding the eggs in the next step.
Slowly add one egg at a time, using a mixer on low speed or a spatula. Be sure to mix each egg thoroughly before adding in the next. Mix together until the batter reaches a thick and smooth consistency. Transfer the dough into a piping bag fitted with a large round tip (You can also cut a small hole in the tip as well).
Prepare a baking sheet with parchment paper or a baking mat, and pipe 2-inch mounds, leaving a few inches apart. Spray the pastry with water with a spray bottle to create a humid environment (you can also wet the baking sheet prior to piping). Using the moisture, smooth down the peaks of each mound.
Bake for 10 minutes, and while the pastries are in the oven, reduce the heat to 350°F and bake for about 20 minutes until golden brown. Do not open the oven door while the pastries are baking, as the cool air will interfere with the rise.
Remove them from the oven and transfer onto a wire rack. Ensure the pastries are cooled completely prior to filling.