Preheat the oven to 400°f / 200°c. Line two baking sheets with parchment paper. Fit a large piping bag with a large round piping tip.
Pate a choux - Take milk, water, butter, vanilla extract, sugar and salt in a pan on medium heat. Once the butter is melted, add in the flour, and start whisking the mixture until it gets incorporated and there are no lumps in the mixture. Stirring constantly, cook the mixture for 2 minutes to help dry it out. Signs to check if the dough is ready or not, includes a thin starchy film forming all over the inside of the pan and the dough pulling together into a cohesive mass.
Transfer the paste to the bowl of a stand mixer fitted with the paddle attachment. Mix on medium speed for 1 minute to help cool down the mixture before adding the eggs.
With the mixture running on low, slowly add one egg at a time. Mix on medium speed for 3-4 minutes, or until the eggs are fully incorporated. The batter should not look stiff. It should look smooth.
Transfer the choux batter to the prepared piping bag. Pipe tiny same sized mounds onto the baking sheet. (If the batter has left a point, you can smooth it down with a wet fingertip)
Remove the craquelin from the freezer and remove the top piece of parchment. Place each circle on top of the piped choux, pressing lightly.
Bake them for 8 mins at 400°F / 200°C, then turn down the oven to 350°F / 180°C, and bake for a further 15-20 minutes, until puffs are deeply golden and puffed up. Remove from the oven and place on a cooling rack to cool completely.