Preheat the Oven:

• Preheat the oven to 400°F (200°C).

• Line a baking sheet with parchment paper.

Make the Choux Pastry:

• In a medium saucepan over medium heat, combine butter, water, sugar, and salt.

• Bring to a boil, then immediately remove from heat.

• Add the flour all at once and stir vigorously until the mixture pulls away from the sides and forms a ball.

Cool and Add Eggs:

• Let the dough cool slightly for 5 minutes.

• Add eggs one at a time, mixing well after each addition until the dough is smooth and shiny.

Pipe the Éclairs:

• Transfer the dough to a piping bag fitted with a large round tip.

• Pipe 3-4 inch long strips onto the prepared baking sheet, leaving space between each.

Bake the Éclairs:

• Bake for 20 minutes at 400°F (200°C), then reduce the oven temperature to 350°F (175°C) and bake for an additional 15-20 minutes or until golden brown and crisp.

• Turn off the oven, prop the oven door open slightly, and let the éclairs cool inside for 15 minutes to dry out.

Heat the Milk:

• In a saucepan, heat the milk over medium heat until just steaming. Do not let it boil.

Whisk the Egg Mixture:

• In a mixing bowl, whisk together egg yolks, sugar, and cornstarch until smooth and pale.

Temper the Eggs:

• Gradually pour 1/2 cup of the hot milk into the egg mixture, whisking constantly to prevent curdling.

Cook the Pastry Cream:

• Pour the egg mixture back into the saucepan and cook over medium heat, whisking constantly until the mixture thickens (5-7 minutes).

Finish the Cream:

• Remove from heat and stir in butter and vanilla extract until smooth.

• Cover with plastic wrap, pressing it directly onto the surface to prevent a skin from forming.

• Chill in the refrigerator for 1 hour.

Heat the Cream:

• In a small saucepan, heat the heavy cream until it begins to simmer.

Make the Ganache:

• Pour the hot cream over the chopped chocolate in a bowl.

• Let it sit for 2 minutes, then stir until smooth and glossy.

• Stir in butter until fully incorporated.

Fill the Éclairs:

• Once the pastry shells are completely cool, use a skewer to poke two holes at the bottom of each éclair.

• Transfer the chilled pastry cream to a piping bag fitted with a small round tip.

• Pipe the pastry cream into each éclair until filled.

Dip in Chocolate Glaze:

• Dip the top of each éclair into the warm chocolate glaze.

• Let excess chocolate drip off and place the éclairs on a wire rack to set.

Chill the Éclairs:

• Refrigerate the assembled éclairs for 30 minutes to set the chocolate.

Serve:

• Serve chilled or at room temperature.