Heat oven to 180ºC fan. Grease and base line a 20 x 30cm brownie tin with baking paper.
Put the chocolate and butter into a bowl over a pan of hot but not boiling water and stir until smooth and melted. Set aside to cool.
Mix together the flour, cocoa, sugar, baking powder and a pinch of salt. Pour the chocolate mixture, mixing well until blended. Add eggs, one at a time, beating well after each addition. Fold in walnuts, mixing only until combined. Do not over mix.
Pour the mixture into the prepared tin and bake for 30 to 35 minutes until firm and done. Cool.
To make the icing, put the butter into a bowl over a pan of hot water over low heat. Stir in the cocoa, add the icing sugar and milk, stir well. Pour and spread over the top of the cake. Scatter and lightly press the walnuts on top. Let it set. Remove carefully from the tin then cut into squares.
Its perfect with ice cream as a dessert!
