Preheat oven to 400°F.
In a small pot, add in the water, butter, sugar and bring to a boil over medium high heat.
Add in the flour at once and reduce the heat to low. Stir the mixture vigorously with a wooden spoon until it forms a ball of dough, about 4-5 minutes. Remove from heat.
Using a stand mixer with a paddle attachment fitted, transfer the dough to the mixer and turn it on low speed. This will help cool down the dough before adding the eggs.
Once the dough is lukewarm, gradually add in the lightly beaten egg in a few additions, but be careful not to add too much egg.
The dough will look curdled between additions, but don't worry, it will absorb the egg. Scrape down the bowl periodically. To check if you've added enough egg, pull up the paddle from the mixture -- if the mixture hanging down from the paddle forms a "v," it's ready. The dough will be shiny and glossy.
Transfer the choux dough to a large piping bag, fitted with a round tip.
Holding the piping tip straight and upright, pipe round dollops about 1.5" in diameter and 1" in height on the prepared baking sheet and leave a few inches in between each dollop. Repeat until all the dough is used up. (Should end up with 10-12 mounds).
Fill a small dish with a little water and wet the tip of your finger to dab down any pointed tops in the choux dough.
Place a frozen craquelin disc on top of each choux dough mound.
Bake the cream puffs at 400°F for 10 minutes.
Lower to 350°F and bake for another 25-30 minutes. Remove puffs from the oven and cut off the tops using a sharp serrated knife. Place them back into the oven with the door slightly ajar and the oven turned off for about 15 minutes to fully dry out.
Remove puffs from oven and let cool on a rack.
At this point in time, cream puffs can be sealed in an airtight container for up to 2 days at room temperature if not using right away.