Line a 20cm x 30cm lamington pan with baking paper. Process biscuits, coconut, nuts and cocoa in a food processor to coarse crumbs. Transfer to a bowl. Melt the golden syrup, 120g chocolate and 2 tablespoons butter in a pan over low heat. Add to crumbs with egg, mix well, then press into pan. Chill until set. Melt remaining chocolate and butter in a small pan over low heat until smooth, then pour over slice. Score top with a knife to form 24 squares. Place an extra nut in centre of each square, then chill until set. Slice and serve drizzled with extra chocolate if desired.