Preheat the oven to 180oC, gas mark 4. Grease and base line a 20cm tin.
Place the butter and chocolate in a large heatproof bowl and place over a saucepan of simmering water until melted, stirring occasionally. Cool slightly.
Meanwhile, place the sugar and eggs in the bowl of the kitchen machine fitted with the whisk attachment. Whisk until pale and thickened and resembles ribbons. Gently whisk in the chocolate mixture.
Sieve the flour and cocoa together and gently fold into the chocolate mixture using the K Beater, taking care not to over stir. Fold in your optional hazelnuts. Pour into the prepared tin and bake for 18-20 minutes until a crust has formed but is still a little soft in the centre. Allow to cool slightly.
To make the meringue, place the egg whites in the bowl of the kitchen machine fitted with the whisk attachment and whisk until soft peaks. Whisk in the sugar, 1 tablespoon at a time until thick and glossy.
Remove the brownie cake from the tin and place on a baking tray, spoon over the meringue giving a rough appearance. Place under a preheated grill for 1-2 minutes or until browned, or use a blow torch.
Great served warm.