There's no Irish or English equivalent to the Italian "crema pasticcera" really. It's a type of custer, but much thicker as either flour or cornflour are used. It is one of the staples of Italian desserts (also in its vanilla version, without chocolate), and it's used as a filling for a variety of cakes or as a spoon dessert.
My basic rule is to use cocoa powder (not sweetened) for cakes, or dark chocolate (70-85%) for spoon desserts.
Ingredients for 900gr of cream (perfect quantity for the filling of 1 cake, 24cm diameter if round, or equivalent), or for 12 x 10cm diameter tarts):
620ml milk (whole milk, or soy/rice milk - if using those though, reduce the amount of sugar by 40gr)
1.5 tsp vanilla paste
3 eggs
100gr caster sugar
45gr cornflour
80gr dark, unsweetened cocoa powder
Ingredients for 1200gr of cream (perfect quantity for 6 dessert bowls containing 200gr each):
830ml milk (whole milk, or soy/rice milk - if using those though, reduce the amount of sugar by 40gr)
2 tsp vanilla paste
3 eggs (or, better: 3 large eggs and 1 medium egg)
130gr caster sugar
60gr cornflour
180gr dark chocolate (70-85%)
Method:
Heat up the milk but don't let it boil, then dissolve the vanilla paste and keep it warm
Using an electric mixer, whisk the eggs at medium speed until frothy but don't let them increase much in volume or change colour
Add the sugar and continue to whisk the eggs at medium speed until the sugar has been fully absorbed, but not for longer
Add the cornflour and the cocoa powder (if making this for cakes) and again continue to whisk at medium speed until fully absorbed
Add the hot milk gradually, starting with the manual whisk, then continuing to whisk at medium speed and until all the milk has been incorporated - at the end increase the whisk speed
Put the pot onto a medium heat, and cook until it is quite thick while whisking all the time with a manual whisk: never leave it for a moment, and towards the end ensure you do not scrape the bottom with your whisk
Once ready, remove from the heat, then use your electric whisk again at high speed until it's all perfectly smoothed out
Now transfer the cream onto a bowl (preferably pre-chilled in the fridge) and cover it with clingfilm, ensuring that the film makes perfect contact with the cream: this will prevent the skin from forming on the cream
If making a spoon dessert:
Chop the dark chocolate quite well
Once the basic cream is ready, take it off the hob and add the chopped chocolate
Whisk with the electric whisk until all chocolate has melted and the cream is quite smooth
Transfer the cream in the individual bowls (preferably chilled in the fridge) and cover each bowl with clingfilm to avoid the skin forming on the cream