1.  Preheat the oven to 400°F (200°C) and line a baking tray with parchment paper. 
2.  Combine water, butter, and salt in a saucepan. 
3.  Bring to a boil until the butter melts completely. 
4.  Add the flour all at once and stir vigorously until a smooth dough forms. 
5.  Cook for 1–2 minutes, stirring constantly, until the dough pulls away from the sides. 
6.  Transfer the dough to a bowl and allow it to cool slightly. 
7.  Add the eggs one at a time, mixing thoroughly after each addition. 
8.  Transfer the dough to a piping bag. 
9.  Pipe long strips onto the prepared baking tray. 
10.  Bake for 25–30 minutes, until puffed and golden. 
11.  Turn off the oven and leave the éclairs inside for 5 minutes with the door slightly open. 
12.  Remove and cool completely. 

Make the Coffee Cream

1.  Heat the milk in a saucepan until steaming. 
2.  Whisk the egg yolks, sugar, and cornstarch until smooth. 
3.  Gradually whisk the hot milk into the egg mixture. 
4.  Return the mixture to the saucepan and cook over medium heat, stirring constantly, until thick. 
5.  Stir in the coffee and vanilla. 
6.  Cover the surface directly with plastic wrap and refrigerate until completely chilled. 

Fill and Glaze

1.  Make small holes underneath each cooled éclair. 
2.  Pipe the chilled coffee pastry cream into the shells. 
3.  Mix powdered sugar, coffee, and vanilla until smooth and glossy. 
4.  Dip the tops of the éclairs into the coffee glaze. 
5.  Refrigerate for 15–20 minutes to set. 
6.  Serve chilled or slightly cool.