Prepare the Choux Pastry:

• Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.

• In a saucepan, combine water, butter, and salt, bringing it to a boil. Once the butter melts, add the flour and stir until the mixture pulls away from the sides of the pan.

• Remove from heat and let it cool for 5 minutes before adding the eggs one at a time, mixing after each addition. The dough should be smooth and glossy.

• Transfer dough to a piping bag and pipe 4-inch long lines onto the baking sheet.

• Bake for 25-30 minutes, then reduce the temperature to 350°F (175°C) and bake for an additional 10-15 minutes. Cool on a wire rack.

Make the Pastry Cream:

• In a saucepan, heat milk over medium heat until steaming.

• Whisk together egg yolks, sugar, flour, and cornstarch in a separate bowl.

• Gradually add hot milk to the egg mixture, whisking constantly. Return the mixture to the saucepan and cook over medium heat until it thickens.

• Remove from heat and stir in vanilla extract. Cover with plastic wrap and refrigerate until cooled, about 2 hours.

Prepare the Chocolate Glaze:

• In a heatproof bowl, combine chopped chocolate, butter, and water. Microwave in 20-second intervals, stirring each time, until smooth. Set aside to cool slightly.

Assemble the Eclairs:

• Once the eclairs have cooled and the pastry cream is chilled, make a slit in each eclair and fill with pastry cream.

• Dip the top of each eclair into the chocolate glaze and let excess glaze drip off.

• Place the eclairs on a serving tray and let the glaze set for a few minutes before serving.