Preheat the oven to 425o degrees and move the oven rack to the middle position. Line two baking sheets with parchment paper.
In a heavy saucepan, add the milk, water, butter, sugar, and salt. Bring to a boil over medium-high heat. Remove the pan from the heat and add the flour, all at once. Stir vigorously with a wooden spoon. Return the pan to medium heat and continue to stir constantly until the mixture starts to form a soft ball and pulls away from the pan and a thin film coats the bottom and sides of the pan - about 3-4 minutes.
Remove the pan from the heat and let the mixture cool for about 2-3 minutes.
Transfer the mixture to the bowl of a stand mixer fitted with the paddle attachment. On low speed, beat for about 2-3 minutes to allow the choux paste to slightly cool. Do not beat the mixture longer than 3 minutes, otherwise, the dough may start to separate.
On medium speed, begin to add the beaten eggs, 1 at a time or 1/4 cup, and beat until fully incorporated before adding the next egg. As you are adding the last egg, add slowly as you may not need all of it. Check your batter for a thick, yet pipeable consistency that is smooth and shiny and it will be 'stringy' when you lift the paddle. Beat for at least 2 minutes after the last egg is added.
Sprinkle the parchment paper on the prepared baking sheets lightly with water. The moist parchment paper creates a nice humid environment for the cream puffs to puff!
Using a small cookie scoop, drop generously sized 2-tablespoon mounds on the baking sheet, spacing 2" apart. You should be able to fit 12 puffs on each baking sheet.
Bake one sheet at a time. Bake for 15 minutes, then reduce the oven temperature to 350o degrees and bake for an additional 15-20 minutes, until golden brown. Do not open the oven door while the cream puffs are baking!
Remove the cream puffs from the oven and cut a small slit on the side of each and return them back to the oven for another 2-3 minutes, this allows the steam to escape so the inside of the puff is not too moist. Place the puffs on a wire rack to cool completely.
Turn the oven temperature back up to 425o degrees, and repeat the process with the second batch.