Add all ingredients into a medium sized bowl, then mash together with a spatula until an uniform looking dough forms.

Place the dough between 2 pieces of parchment paper, then roll the dough out to be about 1/8” thick. Place into the freezer for at least 30 minutes, while you make the choux.

In a medium saucepan over medium heat, add milk, water, butter, 1 tbsp sugar, and salt, and bring to a boil, stirring occasionally. Add flour in the pot, all at once, and begin to stir very quickly. A ball of dough should form relatively quickly. Continue cooking, stirring vigorously, until a dry film begins to form on the bottom and sides of the saucepan. Remove from heat.

Add dough to the piping bag, and pipe directly onto parchment lined baking sheets. Pipe about nine 2” rounds per baking sheet (about 18 total).

Cut out 18 rounds out of the cold craquelin topping, about the same diameter as the piped cream puffs. Place each round onto a piped cream puff, lightly pressing it down to secure it.

In a large sized bowl, whisk together the egg yolks and whole egg. Add in the 2/3 cup sugar and the cornstarch, and whisk well to combine. Set aside.

In a large saucepan over medium heat, bring milk, espresso powder, and ½ cup sugar to a boil, stirring occasionally. Once it begins to boil, remove it from the heat, and very slowly drizzle the hot milk mixture into the egg mixture, stirring vigorously while drizzling. Once all of the hot milk mixture has been added, pour the entire mixture back into the sauce pan and place back onto medium-low heat.

Cook the mixture, stirring constantly, until the mixture has thickened and resembles the thickness of pudding. Add in the chopped chocolate, butter and vanilla, stir and let sit for 5 minutes to allow butter and chocolate to melt. Once melted, stir well to combine everything, then place into a heatproof bowl. Place a piece of plastic wrap over the surface of the custard, so a skin does not form, and place into the fridge to cool completely.