Pastry Cream Filling
1. Get a bowl ready for cooling the pastry cream with a fine mesh sieve on the rim.

2. Pour milk into a heavy saucepan. Split half vanilla bean in half lengthwise and scrape seeds out Into the milk. Add salt and place over medium heat and bring milk to a near boil. To ensure no milk solids stick to the base of the pan, keep scraping the bottom with a spatula.

3. In a medium mixing bowl whisk together sugar and cornstarch. Add eggs and whisk until smooth.

4. When milk is ready slowly ladle about one third of the hot milk into the egg mixture, whisking constantly. Pour the egg-milk mixture back into the hot milk whisk constantly. Whisk over medium heat until the custard is as thick as lightly whipped cream, around 2 minutes. For the cornstarch to thicken fully the mixture must come to a boiling point. You will need to see a few slow bubbles but you need to be careful not to boil too vigorously as it will curdle the mixture.

5. Remove from the heat and pour through the sieve into the bowl. Add in chocolate and stir to melt.

7. Let cool for 10 minutes, stirring occasionally to release the heat and prevent a skin from forming.

8. Once the pastry cream has cooled slowly, mix in the butter one piece at a time, Make sure the butter is fully incorporated before adding the next piece.

9. Cover the pastry cream with glad wrap pressed onto the surface to prevent a skin from forming and cool in the fridge until needed.

Choux
1. Preheat the oven to 220°C. Butter a baking sheet or line it with baking paper.

2. To make the choux paste, in a pot, combine the milk, water, butter, sugar, and salt and place over medium heat until the butter melts and the mixture comes to a full boil. Add the flour all at once, stirring vigorously with a wooden spoon. Keep stirring until the mixture has formed a smooth mass and pulls away from the sides of the pan and some of the moisture has evaporated. This will take about 3 minutes.

3. Transfer to the bowl of a stand mixer fitted with the paddle attachment or to a heat proof mixing bowl. If using a mixer, add the eggs one at a time and mix on medium-high speed, incorporating each egg before adding the next. When all the eggs have been added, the mixture will be thick, smooth, and shiny. If making by hand, add the eggs one at a time and mix with a wooden spoon, incorporating each egg before adding the next.

4. Transfer the contents of the bowl to a pastry bag fitted with a 12mm plain tip, adding only as much to the bag as is comfortable to work with. Pipe out fingers 12 cm long and 2.5 cm wide, spacing them about 5 cm apart. If you end up with a tail at the end of the piping, you can smooth it over with a damp fingertip.

5. Bake until puffed and starting to show some colour, about 10 minutes. Reduce the oven temperature to 190°C and continue to bake until the shells feel light for their size and are hollow inside, about 12 minutes longer. They should be nicely browned all over. Remove from the oven and, using a metal skewer, poke a small hole in the bottom of each shell to allow steam to escape. This keeps the shells from collapsing. Let cool on wire racks.

Glaze
1. Combine the chocolate and corn syrup in a heatproof bowl. Bring the cream to just under a boil in a small saucepan.

2. Pour the cream over the chocolate. Let the mixture sit for about 2 minutes without stirring until the chocolate melts, and then stir gently with a rubber spatula until smooth and shiny. Let cool until just warm.

Fill and glaze the éclairs
1. Stir the pastry cream (it must be very cold) until smooth and then spoon the cream into a pastry bag fitted with a plain tip with a very small opening. It is easiest to start with a hole in each end of the shell and to fill from both ends if necessary. Sometimes pockets inside the shell prevent the pastry cream from filling the entire shell from a single hole. Fill the shells until they feel heavy.

2. To glaze the éclairs, dip the top of each filled éclair into the glaze, shaking gently to allow the excess to drip off, and then place upright on a wire rack and allow the glaze to set. spoon

Alternatively, you can fill the shells by splitting them in half with a serrated knife. Dip the top half in the glaze, allowing the excess to drip off, and then place upright on a wire rack and allow the glaze set. Spoon the pastry cream into the bottoms of the shells and replace the glazed tops.

Serve the pastries at once, or refrigerate for up to 6 hours before serving. They should be eaten the same day they are filled.