In a medium saucepan, bring the water and butter to the just before boiling. Once the butter has me,ted, remove from the heat.
Add the flour quickly and all at once, stir quickly to combine completely.
Return the saucepan to the heat and cook for about 1 to 2 minutes until the dough pulls away from the sides of the saucepan.
Allow to cool for about 5 minutes.
Preheat the oven to 200ºC. Line a large baking tray with baking paper or silicone mat.
Spray the prepared baking.
Beat the eggs and add about a third to the dough and beat well. It will separate at first, continue until it is completely combined.
Continue adding egg until you get a pipable dough with a glossy sheen. You may not use all the egg.
Fill a piping bag with a star nozzle and pipe short lengths of dough onto the prepared baking tray.
Bake for 10 minutes and then turn down the oven to 180ºC and bake for a further 15 minutes. Start 10min timer
Remove the buns from the oven, prick the base with a cake tester or toothpick to release the hot air.
Return to the switched off oven and allow to cool.
Bring the milk to a simmer, tiny bubbles will form around the edge of the saucepan.
While you wait for the milk to heat up, beat the eggs with the flour, corn flour, vanilla and sugar.
Pour half of the warmed milk into the egg mixture, stirring quickly.
Return the remaining milk to the heat and bring to the boil.
Pour the egg and milk mixture into the boiling milk while whisking rapidly and cook until thick.
Place into a shallow dish and cover with clingfilm to cool.
Fill a piping bag with crème pâtissière and a small nozzle.
Pipe crème pâtissière into the base of the choux buns, filling them carefully. They should become heavy.
Place 250ml castor sugar onto high heat in a frying pan. Allow sugar to melt and turn amber. Turn off heat.
Carefully dip the top of each bun into the sugar and set aside.