Put the chocolate, peanut butter, butter and syrup in a saucepan and heat gently until melted, stirring occasionally. Remove from the heat.
Place the biscuits in a plastic bag and crush roughly using a rolling pin. Stir the crushed biscuits and the nuts into the chocolate and stir until evenly coated.
Spoon the mixture into a 20 cm (8 inch) shallow square cake tin lined with nonstick baking paper, and spread the surface level. Chill for 4 hours until firm. Lift the cake out of the tin using the lining paper, cut into 15 small squares and peel off the paper. Decorate with sugared almonds. Store in an airtight tin for up to 3 days.