Preheat oven to 180°C/350°F. Grease a 19cm (8in) square cake pan; line base and sides with baking paper, extending the paper 5cm (2in) above sides.
Combine sifted flour and cocoa, sugar, and coconut in a medium bowl; stir in melted butter until combined. Spoon into pan; use the back of a spoon to press mixture evenly over base of pan.
Bake base for 15 minutes or until golden. Cool.
Place condensed milk, syrup and half of the extra butter in a medium saucepan; cook over medium heat, stirring continuously, for 10 minutes or until caramel is thickened and a golden colour. Working quickly, pour caramel over the base in pan; smooth the surface level with a spatula. Press peanuts into caramel with a spatula. Bake for 10 minutes; cool.
Place chocolate and remaining extra butter in a medium heatproof bowl over a medium saucepan of simmering water (don’t let water touch base of bowl); stir until chocolate melts. Pour chocolate mixture over caramel layer. Cool slice completely before removing from pan and cutting into pieces.
Slice will keep refrigerated for up to 1 week.
You can omit the peanuts or swap them for coarsely chopped macadamias or roasted peeled hazelnut halves, if preferred.Note