Put the butter in a heatproof bowl with the cocoa powder, chocolate buttons and golden syrup. Sit over a pan of simmering water and stir until melted. Remove from the heat and set aside to cool.
Crumble in the wholewheat biscuits and stir gently. Divide the chocolate mixture between 9 shallow paper cake cases placed in a 12-hole cake tin. Make a slight dip in the middle of each nest and press in 3 chocolate eggs in each. Leave to set in the fridge for 1 hour.
Cook's tip: you could use jelly beans as an alternative to mini eggs.