Cooking oil spray, to grease
200g brown sugar
250g caster sugar
325g unsalted butter, chopped
125g Dutch cocoa
1 tsp vanilla extract
150g hazelnuts, toasted, skinned, roughly chopped
100g dark chocolate, chopped
250g plain flour
2 tsp brandy or hazelnut liqueur
Chocolate-hazelnut spread, to serve
Preheat oven to 150°C. Grease a 30 x 23cm rectangular cake tin with cooking oil spray, then line base and sides with baking paper.
Put sugar and eggs in the large bowl of an electric mixer and beat on high, using whisk attachment, until pale and thick.
Meanwhile, put butter in a small saucepan over a low heat and stir until melted. Stir in cocoa, then transfer to a large mixing bowl.
Fold sugar mixture into butter mixture. Stir in vanilla, ½ of the nuts, chocolate, flour and brandy or liqueur. Pour into prepared tin and press firmly with a spatula to smooth surface. Scatter over remaining nuts.
Bake for 25 minutes. Remove from oven and allow to cool completely in tin. Slice and serve with chocolate-hazelnut spread.