In a saucepan, combine unsalted butter, water, whole milk, granulated sugar, and salt. Heat until simmering, then add bread flour and whisk until a smooth dough forms.

Cook for 3-5 minutes until the dough pulls away from the sides, then transfer to a mixer to cool slightly before adding eggs.

Once the dough has cooled for about 5 minutes, gradually mix in eggs, one at a time, using medium speed until the dough is glossy.

Chill the choux pastry for about 30 minutes. Fit a pastry bag with a star nozzle and pipe eclair shapes on a baking mat.

Dust lightly with powdered sugar and place in the freezer for at least one hour.

Preheat your oven to 200°C (392°F). Place the chilled eclairs in the oven and reduce the temperature to 170°C (338°F). Bake for 40 minutes.

Remove eclairs from the oven and let them cool on a wire rack.

Ensure they cool completely before filling them with pastry cream.

In a bowl, whisk together egg yolks and granulated sugar until fluffy, then gradually mix in cornstarch and flour.

Heat whole milk in a saucepan, pour into egg mixture while whisking to prevent curdling.

Return combined mixture to medium heat, stirring continuously until thickened, about 5-7 minutes.

Remove from heat and mix in butter and vanilla extract until smooth.

Heat heavy cream until simmering, then pour it over semi-sweet chocolate. Whisk until smooth and allow to cool.

Fill each cooled eclair with vanilla pastry cream using a pastry bag.

Dip the tops of each filled eclair into the chocolate ganache.

Arrange the Classic Chocolate Eclairs on a serving platter and serve immediately.