For pastry cases, preheat oven to 190°C (fan forced), grease and line two baking trays with baking paper.
Place water, sugar, salt, and butter into a saucepan over medium heat and stir to melt the butter. When water starts to boil, remove saucepan from stove and add the flour in one go. Stir vigorously with a wooden spoon. When the flour has absorbed the water, return the saucepan to the stove.
Cook the dough 1-2 minutes over medium heat, stirring until a ball is formed and it pulls away from the sides of the saucepan. If the dough is not thick enough, cook for a further 1 minute.
Transfer the dough into a bowl and allow to cool for 10 minutes. Add the vanilla extract and then with a hand-held mixer, mix the dough while adding the eggs one at a time, mixing well after each addition.
Place dough into a piping bag, or use a teaspoon and pipe or spoon 2 teaspoons of dough, 5cm apart on each tray. With a damp finger, flatten the peaks on any of the profiteroles for a rounded shape.
Bake 2 trays at a time for 30 minutes. Remove from oven, prick each shell with a skewer and return to the oven to dry out for another 5-7 minutes.
Remove form oven, transfer to a rack, and allow to cool down completely before filling profiteroles with custard and drizzling with chocolate sauce.
For custard filling, in a medium size bowl, whisk together the egg yolks and sugar. Then add corn flour and cocoa powder and mix well.
In a medium saucepan over medium heat, add milk, sugar and vanilla and heat until it starts to simmer.
Slowly add hot milk mixture to the egg and sugar mixture whisking well between each addition. Pour mixture back into the saucepan and whisk continuously until the mixture becomes a thick custard consistency.
Remove from heat, pour into a bowl, and press cling wrap into the surface to stop it from skinning over. Refrigerate for 3-4hours until set.
Spoon custard into a piping bag fitted with a small nozzle and fill each profiterole with the custard.
For ganache, in a microwave safe bowl, add chocolate and cream. Microwave for 30 seconds at a time, four times, stirring in between until well combined and a smooth consistency for dipping.
Dip each profiterole into the chocolate sauce. For an extra Easter treat, top each one with a chocolate egg.