Make the Choux Pastry
In a saucepan, heat water, butter, and salt until boiling. Remove from heat and stir in flour until a dough forms. Return to low heat for a minute to dry slightly. Transfer to a bowl and add eggs one at a time, beating until smooth.
Pipe the Éclairs
Preheat oven to 200°C / 400°F. Fill a piping bag with dough and pipe 4-inch logs on a parchment-lined baking sheet. Keep them evenly spaced.
Bake to Golden Perfection
Bake for 15 minutes at 400°F, then lower to 180°C / 350°F for 20–25 minutes. Do not open the oven early! Let them cool completely before filling.
Prepare the Chocolate Pastry Cream
Heat milk until steaming. Whisk egg yolks, sugar, and cornstarch in a bowl. Temper yolks with hot milk, then return to heat and cook until thickened. Remove from heat, stir in chocolate and vanilla until smooth. Chill before using.
Fill the Éclairs
Cut a small slit in each éclair or use a piping bag with a tip. Fill generously with chocolate pastry cream. Don’t be shy—this is the best part.
Make the Ganache
Heat cream until just simmering. Pour over chopped chocolate and butter. Stir until glossy and smooth. Let it cool slightly.
Top the Éclairs
Dip the top of each filled éclair into ganache or drizzle artistically. Let set for a few minutes.