Place the heavy cream, chocolate, and oil in a microwave safe bowl.
Microwave in 15-30 second bursts, stirring after each one, until all the chocolate has melted.
Add the vanilla extract and stir until glossy and smooth.
Assemble the cake
Place one cake layer on a plate or cake dish.
Pile the chilled custard in the center of the cake and spread it outwards toward the edges of the cake. Don’t spread it all the way. Leave about half an inch around the edge of the cake plain. This leaves room for the custard to spread out more when the top cake layer is added.
Place the second cake layer on top of the custard and very gently press down to secure it on the custard.
Stir the glaze, it should be thick but still pourable. If it is too thick to pour, reheat it five seconds at a time, stirring after each time, until it is pourable.
Pour the glaze on the center of the top cake layer and use an offset spatula or large spoon to spread it outwards to the edges of the cake, allowing it to drip down the edges in places. Don’t spread it too thin, the cake shouldn’t be visible through the glaze and the glaze should look smooth and shiny.
Place the cake in the fridge for 30 minutes to set the glaze.