Preheat the oven to 425°F and line baking sheet(s) with parchment paper. This recipe makes about 24 puffs so it will take 3 batches to bake with 8 puffs per baking sheet.
Add the water, milk, butter, sugar, and salt to a medium saucepan on the stove and mix over medium to high heat. Bring to a boil and then remove from heat. Add flour and quickly stir into the mixture. It really starts to form more of a dough at this point.
Return the pan to the stovetop on medium heat and stir constantly for a few minutes, cooking until mixture pulls away from the pan and a film forms on the bottom of the pan. This happened pretty quickly for me.
Transfer the dough to a stand mixer or bowl and beat on low speed for 3-4 minutes until the mixture has cooled. Add the eggs, one at a time, and beat on medium speed until each is fully mixed in. Mix until shiny and almost ribbon like.
Place the dough in a pastry bag with a round tip. Pipe round circles spaced at least 1 inch apart on the prepared baking sheet. Try not to pull up and leave a peak, but you can smooth down with your finger if needed.
Place one baking sheet at a time in the oven and bake for 15 minutes. Lower the oven temperature to 375°F and continue baking for another 5-10 minutes, until golden and airy. Keep an eye on them because they brown quickly! Remove from the oven and transfer to a wire rack to cool. Repeat step 5 for the rest of the pastry dough and make sure your oven heats back up to 425°F before the next pan goes in.