In a medium saucepan, combine the water and unsalted butter. Bring this mixture to a boil over medium heat.

Stir in the flour and salt, mixing until a smooth dough forms. Cook for a couple of minutes until it’s pulling away from the sides of the pan.

Remove from heat and let it cool for about 5 minutes.

Add the eggs one at a time, mixing well after each addition until you have a thick and shiny dough.

Preheat your oven to 425°F (220°C) and line two baking sheets with parchment paper.

Transfer the dough to a piping bag fitted with a large round tip. Pipe 3 to 4 inch long lines onto the prepared baking sheets, ensuring space between each one.

Bake for about 20 minutes or until golden brown and puffed up.

In a saucepan, whisk together the milk, sugar, and cornstarch. Bring it to a simmer, stirring constantly until it thickens (about 5 minutes).

In a bowl, whisk the egg yolks and slowly add some of the hot mixture to temper them.

Pour the tempered egg yolk mixture back into the saucepan and cook for another few minutes until thickened. Remove from heat.

Stir in the coffee, vanilla, and butter until smooth.

Transfer the cream to a bowl, cover it with plastic wrap directly on the surface to avoid a skin forming, and chill in the fridge for at least an hour.

Melt the chocolate chips and heavy cream together in a bowl, either in the microwave or over a double boiler, until smooth and glossy.

Once the shells are cooled, use a small knife to pierce the side gently. Fill them generously with the chilled mocha pastry cream using a piping bag.

Dip the top of each éclair in the chocolate glaze and let it set for a few minutes.