Melt the butter and chocolate in a pan on a low heat. Remove the pan from the heat, add the chilli, let the mixture cool a little.
Make the mixture
Beat the egg yolks, sugar and salt in a bowl until the mixture turns paler in colour, halve the mixture. Combine the cream cheese, lemon zest and icing sugar and fold into half the mixture. Combine the other half with the chocolate and crème fraîche.
Make the brownies
Mix together the nuts, flour and baking powder and divide evenly between the two halves of mixture, stir in. Spoon 2/3 of the pale mixture into the prepared tin and top with the dark mixture. Then spoon the remaining pale mixture on top in batches and, using a wooden skewer, create an even marbling effect.
For approx. 25 mins. in the bottom half of an oven preheated to 180°C. The brownies should still be a little gooey inside. Remove from the oven, allow to cool a little, cut into squares, remove from the tin and leave to cool on a rack.