Line two baking trays with parchment paper. Using a 1-inch round stencil, a pastry tip or bottle cap, trace out 70 circles using a pencil or pen, 35 circles per tray. Flip the sheets of parchment over so there isn't any transfer to the profiteroles. Set trays aside until ready to use.
Preheat the oven to 425 degrees Fahrenheit and arrange the racks on the upper and lower thirds of the oven.
In a sauce pan over medium heat, add the milk, sugar, salt, butter, and water. Bring the mixture to a simmer using a wooden spoon to help the butter melt.
Once the mixture starts bubbling, add the flour all at once and stir with the wooden spoon. Once the flour has been incorporated, stir vigorously until everything comes together into a soft dough and there's a light film on the bottom of the sauce pan.
Continue to cook the dough over medium heat, vigorously beating the dough against the sides of the pan until the film on the bottom has reabsorbed into the bowl and the dough holds together in a ball, around 3 minutes
Transfer all of the dough into the bowl of your stand mixer with the paddle attachment. Let the dough sit for a minute or two then mix for 30 seconds to help cool the dough slightly.
On low-medium speed, add the eggs to the mixture one at a time. After each egg the mixture will look glossier and looser than before. After the fourth egg, check the consistency of the mixture. It needs to be thick enough to hold its shape but loose enough that when you pull the paddle out of the dough, it forms a V shape when it falls off the paddle. Add the fifth egg if needed to get the right consistency.
Transfer the mixture to a piping bag. Shake the bag a few times to get any air bubbles out and twist the bag to close.
Cut a 1/2" hole in the bottom of the pastry bag. Place the tip of the pastry bag in the center of one of the circles and press the dough out, not moving the bag until the circle has been filled in with dough. Repeat for the rest of the circles.
Take the craquelin rounds out of the fridge and press the rounds onto the tops of the piped pastry dough.
Place one baking tray in the lower rack of the oven and the other in the upper rack. Reduce the temperature to 375 degrees Fahrenheit. Bake for 20 minutes and switch the trays in the oven. Bake for another 10-15 minutes or until the puffs have risen and are a deep golden brown.
Turn the oven off and leave the puffs inside to cool for 15-20 minutes. Prop the oven door open to help cool the puffs slowly. Remove the pastry cream from the fridge so it can start warming up.
Remove the puffs from the oven and using a small paring knife, poke a hole in the bottom of each puff to allow steam to escape. Let the puffs cool completely on the baking trays.
Take the bag of pastry cream and insert the tip into the bottom of one of the puffs and squeeze the bag to fill. The cream puffs should be sufficiently filled but not so much that they're bursting. Repeat with the other 69 cream puffs.