For the Choux Pastry:

• 1 cup water
• 1/2 cup unsalted butter
• 1/4 teaspoon salt
• 1 cup all-purpose flour
• 4 large eggs

For the Custard Filling:

• 2 cups whole milk
• 1/2 cup granulated sugar
• 1/4 cup cornstarch
• 4 large egg yolks
• 2 teaspoons vanilla extract

For the Chocolate Ganache:

• 6 ounces semisweet chocolate, chopped
• 1/2 cup heavy cream

Making the Choux Pastry

1. Preheat your oven to 425°F (220°C) and line a baking sheet with parchment paper.
2. In a saucepan, combine water, butter, and salt. Bring it to a boil over medium heat.
3. Remove the saucepan from heat and add the flour all at once. Stir vigorously until the mixture forms a smooth ball.
4. Transfer the mixture to a mixing bowl and let it cool for a couple of minutes.
5. Add the eggs, one at a time, beating well after each addition until the dough becomes smooth and shiny.
6. Transfer the dough to a piping bag fitted with a plain tip.
7. Pipe the dough onto the prepared baking sheet, forming 4-inch-long (10 cm) strips, leaving space between each strip.
8. Bake for 15 minutes, then reduce the oven temperature to 375°F (190°C) and bake for an additional 20 minutes until the eclairs are golden brown and puffed up.
9. Remove from the oven and let the eclairs cool completely.

Preparing the Filling

1. In a saucepan, heat the milk over medium heat until it starts to simmer. Remove from heat.
2. In a mixing bowl, whisk together the sugar, cornstarch, and egg yolks until well combined.
3. Slowly pour the hot milk into the egg mixture, whisking continuously to prevent lumps.
4. Pour the mixture back into the saucepan and cook over medium heat, stirring constantly, until it thickens and reaches a pudding-like consistency.
5. Remove from heat and stir in the vanilla extract.
6. Transfer the custard to a bowl and cover it with plastic wrap, ensuring that the plastic wrap touches the surface of the custard to prevent a skin from forming.
7. Let the custard cool to room temperature.

Assembling the Eclairs

1. Using a sharp knife or a pastry tip, make three small holes on the bottom of each eclair.
2. Transfer the custard filling to a piping bag fitted with a small round tip.
3. Insert the piping tip into one of the holes and fill the eclair with the custard until it feels slightly heavy.
4. Repeat the process for all the eclairs.

Chocolate Ganache Topping

1. Place the chopped chocolate in a heatproof bowl.
2. In a small saucepan, heat the heavy cream over medium heat until it starts to simmer.
3. Pour the hot cream over the chocolate and let it sit for a minute.
4. Gently stir the mixture until the chocolate melts completely and the ganache becomes smooth and glossy.

Serving and Enjoying

1. Dip the top of each eclair into the chocolate ganache, ensuring that the entire surface is coated.
2. Place the eclairs on a wire rack to allow the ganache to set.
3. Serve the chocolate eclairs on a platter and enjoy their irresistible taste and delicate texture.

Tips and Variations

• For a twist on the classic chocolate eclairs, you can experiment with different flavors for the custard filling, such as coffee, pistachio, or raspberry.
• To add a crunchy texture, you can sprinkle some chopped nuts or grated chocolate on top of the ganache before it sets.
• For a more decadent experience, drizzle some caramel sauce over the finished eclairs.