Place the biscuits in a plastic bag and
crush with a rolling pin. Melt the butter or margarine in a pan, then
stir in the sugar and syrup. Remove from the heat and stir in the
biscuit crumbs and cocoa. Turn into a greased and lined 18 cm/7 in
square cake tin and press down evenly. Leave to cool, then chill in
the fridge until set.
Melt the chocolate in a heatproof bowl set over a pan of gently
simmering water. Spread over the biscuit, marking into lines with a
fork while setting. Cut into squares when firm.