Prepare two sheet pans with grease or parchment paper.
Preheat oven to 425°F / 220°C. (400°F Convection if you're doing two pans in one oven)
Weigh out the flour into a small bowl and set aside.
In a small stock pan bring the milk, water, salt, sugar, and butter to a rolling boil. Remove from the heat and immediately add the flour and stir to combine completely into a ball. Put into bowl of a stand mixer and let sit until an instant read thermometer put into multiple places registers less than 125°F / 52°C. Be patient. This is so you don't make scrambled eggs. (Note: Put into the bowl and put the bowl into the mixer so it's off the counter and airflow can go around it. You can spread out the dough a little to cool faster, too.)
With the mixer running on low-medium add one egg at a time. Incorporate each egg fully before adding the next. Won't look very good at first but will come together by the time you've added all the eggs. Beat for another minute or so after adding the last egg and you'll have a smooth batter.
Put a ½" tip (Wilton 2A I think) on a piping bag. Fill the piping bag with the batter and pipe out ~2"-diameter puffs, leaving a 1½"-2" between them. I use a Silpat designed for Macarons that has guides. Just a thought. My piping bags aren't huge so I did this in two batches. You should get 12-15 puffs per sheet pan.
Important: During baking, don't open the oven door.
Put puffs in the 425°F / 220°C oven. Bake for 15 minutes.
Reduce temperature to 350°F/175°C (or 325°F Convection) and 10 minutes, turn the oven on to 350°F / 175°C and bake another 20-25 minutes until golden brown.
Remove the puffs from the oven and use a toothpick to poke a hole or two near the top to allow steam to escape.
Return puffs to the oven for another 5 minutes.
Remove from oven and transfer to a wire rack to cool completely before filling.