Preheat your oven to 400°F (200°C). In a medium saucepan, combine water, unsalted butter, and salt. Bring this mixture to a boil over medium heat.

Once boiling, add the all-purpose flour quickly, stirring vigorously until the dough pulls away from the sides of the pan.

Remove the saucepan from heat and let it cool slightly. Add the eggs one at a time, mixing well until the dough is smooth and glossy.

Use a piping bag to pipe 3-inch logs of dough onto a baking sheet lined with parchment paper.

Bake for about 25-30 minutes until golden and puffed. Allow them to cool completely.

In a saucepan, heat whole milk and heavy cream over medium heat until steaming.

In a separate bowl, whisk together the granulated sugar, egg yolks, all-purpose flour, espresso powder, and a pinch of salt.

Gradually pour the hot milk mixture into the egg yolk mixture while whisking.

Return this combined mixture to the saucepan, cooking over medium heat until it thickens, stirring constantly.

Remove from heat and stir in vanilla extract. Transfer to a bowl, covering it with plastic wrap directly on the surface to prevent a skin from forming. Let it cool in the refrigerator.

In a heatproof bowl, combine the dark chocolate, heavy cream, espresso powder, and unsalted butter.

Melt in the microwave or over a double boiler until smooth and glossy. Stir well and set aside to cool slightly.

Once the pastry and cream have cooled, carefully slice the choux pastries in half lengthwise.

Fill a piping bag with the coffee pastry cream and generously fill each éclair shell.

Replace the top halves and dip the assembled éclairs in the mocha glaze, allowing excess glaze to drip off.

Place on a serving platter.

Your Mocha Éclairs are now ready to be enjoyed! Serve them fresh for the best taste.