Begin by making the custard.Place the milk into a saucepan and bring to the boil. In the meantime, place the caster sugar, vanilla bean paste, eggs and cornflour into a bowl and whisk together.
Once bubbles start to appear in the milk, turn off the heat.
Add a ladle of the hot milk to the egg mixture and whisk well, then add a second ladle and whisk again.
Pour the remaining milk into the eggs and whisk well then return to the pan over a medium heat stirring until it has thickened.
Once thickened stir in the chopped chocolate and stir until melted and combined and smooth.
Pour into a bowl and cover with clingfilm ensuring the film sits on top of the custard to prevent a skin forming.
Place in the fridge to chill for a few hours.
Whisk the cream and sugar until it forms soft peaks then chill until ready to use.
Slice the swiss roll into 8-10 slices.
Place them upright around the edges of the trifle dish and along the base of the dish.
Spread a layer of the chocolate custard on top of the sponge followed by a layer of the whipped cream.
Add a second layer of sliced swiss roll but flat layers then top again with the custard and finally a deep layer of the whipped cream.
Grate over chocolate and decorate with individual chocolates.
Chill in the fridge until ready to serve.