Gently heat the custard and chocolate together in a saucepan over a medium heat. Stir until the chocolate has completely melted into the custard. Cover the surface with cling film to stop the custard forming a skin, then leave it to cool.
Drizzle the chocolate custard into sundae glasses.
Distribute the chopped brownies evenly into the glasses.
Crush the Maltesers a little, then sprinkle about three-quarters of them over the brownies.
Next, spoon the rest of the cooled chocolate custard over the top of the brownies.
Make the final layer adding caramel whipped cream. Cover and chill until you’re ready to serve.