In a food processor, process the flour, baking powder, brown sugar, butter, and almond meal until the mixture resembles breadcrumbs. Add the melted chocolate and process again to form a smooth dough.

Press the mixture into the prepared tin and prick with a fork. Bake for 15 minutes or until the top starts to feel firm. Set aside to cool.

In a medium saucepan, combine the condensed milk, golden syrup, butter, and caster sugar. Stir over a medium-low heat until smooth and golden.

Stir in the toasted hazelnuts, then pour the caramel over the cooled base. Refrigerate for 1 hour or until firm.

Dot spoonfuls of the melted dark chocolate onto the caramel layer, leaving 2cm gaps between each. Fill the gaps with the melted white chocolate. Then use a small palette knife to swirl the chocolates together in a zig-zag motion to create a marbled effect.

Chill the slice in the fridge for at least two hours to set the chocolate. Take the slice out of the fridge 10 minutes before cutting to prevent the chocolate from cracking. Cut into small squares or bars to serve.