Line a 15x20cm shallow baking tin with non-stick baking parchment.
Place biscuits into a large freezer bag and crush with a rolling pin into evenly-sized pieces.
Put the butter and sugar into a pan and melt over a low heat.
Add the cocoa to the pan and stir well.
In a separate bowl, beat the eggs until frothy, then add to the pan.
Add the crushed biscuits to the mixture and mix well, until all the biscuit is coated.
Save a few Maltesers to push into the top, then add the rest of them to the mixture and pour into a greased baking tin.
Smooth the top, then push the remaining Maltesers into it and place the cake tin in the fridge until it is set.