Preheat the oven to 400°F and line a baking sheet with parchment paper.
In a small pot on medium heat, bring the butter, water, milk, and red gel food colouring to a simmer. It is at the right temperature when small bubbles start coming to the surface.
Add in all of the flour at once and quickly stir together until it becomes a soft dough.
Keep cooking the dough on medium heat for about 3-4 minutes to dry it out. Use a spatula to stir it around, break it apart, and reform it into a dough. It should look like dry mashed potatoes.
Let the dough cool in the pot or transfer to a bowl for faster cooling until warm to the touch.
Add the egg to the dough in three parts, stirring thoroughly after each addition until the egg has been “absorbed” by the dough. It might look like it’s curdling at first but just keep stirring.
The dough is right the right consistency when it’s smooth and glossy. Scoop up some dough with your spatula and let it drop back into the bowl. The dough should leave a V-shaped triangle of dough hanging off the spatula.
Use a 2” cookie scooper to scoop mounds of dough and place them on the lined baking sheet leaving at least 2” in between each mound.
Take the craquelin out of the freezer. Use a 2” round cutter to cut rounds out of the craquelin sheet. Place the rounds on top of each mound of choux dough.
Bake at 400°F for 5 minutes then turn down the oven temperature to 350°F and continue baking for another 25-30 minutes until the walls are stiff. A few minutes before they’re finished baking, use a chopstick to poke a small hole in the top of each puff to let the steam out (this will also be the hole to insert the chocolate stems later). Let cool completely before filling.