For the cream:
Bring the milk to a boil.
In a bowl, whisk together the sugar, flour, and egg yolks until the mixture is white.
Pour in the hot milk and continue to mix with a whisk without beating, until the mixture is homogeneous.
Add the instant espresso coffee and mix again.
Transfer the mixture to a saucepan with a thick bottom over low heat, stirring constantly until it thickens.
Pour into a bowl and cover with plastic wrap placed directly on the cream, to prevent a skin from forming. Refrigerate.
For the choux pastry:
Preheat the oven to 375°F (190°C).
Bring to a boil the water, salt, and butter.
Remove from heat and add the flour a little at a time, mixing.
Mix with a wooden spoon until the dough is smooth and homogeneous.
Return to the heat and work the dough until it comes away from the sides of the pan.
Remove from heat again and incorporate the eggs one by one.
When the dough is ready, place it on your work surface and let it cool.
Fill a piping bag with a 1 cm diameter round tip with the choux pastry.
Shape sticks of 8 to 10 cm in length on the parchment-lined baking sheet.
Bake for 20 to 30 minutes, until golden brown. Let cool.
With the tip of a knife, make two holes in the bottom of each cooled cream puff.
Fill with coffee cream through these holes. Glaze the top of the cream puffs with a spatula, following the product’s instructions.