Preheat oven to 200°C and line two baking trays with baking paper.
For the choux pastry, place the water, butter and salt into the TM bowl and cook 3 min/100°C/speed 1.
Add the flour and baking powder and combine 1.5 min/speed 4.
Remove the measuring cup and allow the mixture to cool to 50°C (temperature will be displayed on the Thermomix).
Set the TM to 2 min/speed 5. Meanwhile, add the eggs very slowly through the hole in the lid. Mix a further 1 min/speed 5.
Fill a piping bag with the choux mixture and using a plain nozzle pipe about 12-16 Eclairs onto the lined baking trays. Do not pipe them too close or they will merge.
Bake the Eclairs 30-35 minutes. DO NOT attempt to open the oven while they are baking - they will collapse immediately and you will end up with flat Eclairs. Once baked, leave them to cool on the tray.
Meanwhile, make the custard. Measure the milk, egg, caster sugar, salt, cornflour, scraped out vanilla pod and contents of pod into the clean and dry TM bowl. Cook 8 min/90°C/Reverse/speed 3.
Pour the custard onto a large serving platter (removing the vanilla pod), cover with plastic wrap to avoid a skin forming on top, and allow to cool.
Fill a piping bag with the cooled custard and using a long, thin nozzle, inject each Eclair from both ends with the custard. You will feel it filling up.
Finally, for the ganache, place the chocolate into the TM bowl and blitz 10 sec/speed 9. Melt 5 min/37°C/speed 1. Add the cream and stir 20 sec/speed 2.5.
Pour ganache into a shallow dish that fits the length of an Eclair. Dip the top of each Eclair into the ganache and leave to set on a wire rack. Enjoy!