Preheat oven to 425F/218C. Line 2 baking sheets with parchment paper or silicone mats; set aside. Also, prepare a large pastry bag with a French star tip, I used #8FT.

Prepare the eclair shells first. In a medium-sized sauce pan, combine the water, butter and salt. Melt the butter completely and bring the mixture to a simmer over medium heat. Once simmering, add all of the flour at once. Using a spatula, stir the dough together until it pulls together into a ball, about 1 minute. Transfer the dough in a large mixing bowl and allow it to cool for about 5 to 7 minutes, until warm to touch.

Once dough has cooled slightly, begin whisking in 1 egg at a time. After adding the last egg, keep mixing until mixture is smoothing and uniform. Transfer the dough into the prepared pastry bag and pipe onto baking sheets in 4 to 6-inch logs. Try to pipe the dough evenly, applying equal pressure for an even eclair.

Bake the eclairs at 425F for 10 minutes, then reduce the oven temperature to 350F/177C and bake for an additional 30 minutes. DO NOT OPEN oven door while baking! This will cause the eclairs to fall flat! Check the eclairs for a rich golden color through the oven door. Once eclairs are baked, gently transfer them onto a cooling rack to cool completely. Once eclairs are cooled, poke 2 to 3 holes into the bottom of each eclair with a small pastry tip to add the filling.

While eclairs are baking, prepare the coffee custard. In a large bowl, whisk together the egg yolks and 1/3 cup sugar until pale and thick. In a separate bowl, create a slurry with the cornstarch and water. Add the mixture to the egg yolks and sugar.

In a sauce pan, combine the milk and flour and heat over medium heat until steaming hot. Add the hot milk to the egg mixture in small amounts, whisking after each additional until all of the milk is added. Transfer the mixture back into the sauce pan and cook over medium heat, stirring constantly, until the mixture thickens into a custard. Once the mixture has thickened, add the Kahlua and instant coffee; stir until the coffee is completely dissolved.

Transfer the coffee custard into a large bowl, cover the top with plastic wrap and cool completely in the refrigerator. Once cooled, use a mixer to whisk air into the custard, then gradually add the 1/4 cup softened butter, 1 tablespoon at a time, until a light cream forms. Transfer the cream into a pastry bag tipped with a filling tip (I used Wilton #230).

Pipe the coffee custard into each eclair, filling them completely on the inside. You should feel the eclair expand slightly as you fill it.

Prepare the chocolate glaze last. Heat the heavy cream until steaming hot, then pour over the chocolate chips. Stir until the chocolate glaze is completely smooth. Dip the top side of each eclair into the chocolate, tapping off any excess chocolate. Set them down onto a wire rack for storage.

For garnishing, use white chocolate or gold sprinkles. If adding the white chocolate, transfer it into a disposable bag the pipe thin lines onto the top; do this while the chocolate has not yet set. Run a toothpick lengthwise to create the design pictured above.

If not serving eclairs right away, keep them refrigerated.