Crumble the cake into a large bowl, then continue to crumble between your fingertips until it has the consistency of breadcrumbs.
Add the buttercream icing and mix together with your hands until it starts to come together in a kind of dough.
Break the dough into walnut sized pieces and roll into smooth balls.
Place the cake balls on a plate and pop in the freezer to cool while you melt the chocolate.
Break the chocolate into small pieces and place it in a microwave safe bowl.
Melt the chocolate in the microwave in 30 second bursts, stirring between each one to ensure it melts evenly, until just melted and smooth.
Use a spoon to dip the cake balls into the chocolate to coat, then pop them back on the plate.
Working quickly, top with sprinkles if wanted, then repeat until all the cake balls have been coated in chocolate.
Pop in the fridge for 15 minutes until the chocolate has completely set.