In a bowl, mix the flour, sugar and salt.
Heat up the milk, water and butter in a saucepan on high heat until the mixture is boiling.
As soon as it begins to boil, pour in the bowl of dry ingredients and mix briskly with a spatula or a wooden spoon.
Continue to mix the dough over medium heat to solidify it. This is a very important step.
Then remove from heat and add in the eggs one at a time.
As this step can be long and tiring, you can make it easier by using a food processor.
You must ensure that each egg is completely incorporated before adding the next one.
You should get a soft puff pastry.
To bake it, put the dough in a piping bag with the largest smooth tip you have and evenly pipe the pastry into small puffs on a tin covered with buttered parchment paper. If you don't have a piping bag, you can also use two spoons.
Bake at 170°C or 350°F for 15 to 25 minutes depending on the size of your puffs. Here, we let them cook for 20 minutes.
You should never open the oven while cooking, or your puffs might collapse.
Then turn off your oven. Be mindful that you should let the puffs rest in the hot oven after cooking. Then cool them down at room temperature before filling them with pastry cream or another filling.