In a standing mixer combine all the dry ingredients: flour, sugar, cocoa powder, baking powder, baking soda and salt
Turn the mixer on low and pour the hot water and vegetable oil in. Turn off the mixer after you have poured both in.
Add the eggs and stir until just combined.
Turn the mixer on low again and pour the buttermilk in. Add the vanilla extract in after.
Continue mixing until the batter is smooth.
Pour the batter evenly into a giant cupcake pan that has been lined with 12 fluted baking cups.
Bake for 30 minutes.
Remove the cake and allow to cool in the pan. Once cooled, remove.
Custard
In a medium saucepan, combine heavy cream, milk, and sugar. Turn the heat up to medium-high and allow the cream mixture to scald but not boil.
While the cream is cooking, whisk the egg yolks into a small bowl.
Now, you are going to temper the egg yolks. Get a 1/4 measuring cup and scoop up some of the hot cream. Slowly pour the hot liquid into the egg yolk while you whisk rapidly.
Repeat this process until you have done it a total of 4 times. Adding 1 cup of hot liquid into the egg yolks.
Slowly pour the egg yolk mixture into the saucepan while you whisk the hot cream.
Allow the cream mixture to simmer and thicken.
Add the vanilla extract and the pinch of salt. Whisk the mixture.
In a small bowl combine the cornstarch and water. Whisk until smooth.
Slowly pour the cornstarch into the hot custard while you are whisking.
Allow the mixture to cook until thick. Remove from heat.
Strain the custard through a sieve into a bowl.
Cover the custard and place it in the fridge to chill. You must chill for at least 4 hours.
Ganache
In a microwave-safe bowl, combine the chocolate chips & cream. Microwave for 30 seconds.
Stir rapidly. Repeat the heating cycle with another 30 seconds.
Stir again. Continue stirring until smooth. If necessary, microwave for 30 more seconds. Be careful not to burn your chocolate.
Assemble
Take chilled custard and spoon it into a piping back with a Wilton 12 piping tip.
Carefully insert the tip into each cupcake and squeeze the custard in until the cupcake looks a bit chubbier. Be careful not to squeeze in too much or else it will all come pouring back out. Once you feel a bit of resistance, you are done.
With a frosting spatula, spread the warm ganache on top of the filled cupcake. Allow the ganache to set before serving.