Directions: 1. Melt chocolate and butter in a saucepan over a low heat, taking care not to overheat. Remove from heat and stir in vanilla essence.
2. Beat eggs and sugar together until thick and creamy. Fold through chocolate mixture. Sift flour and baking powder over chocolate mixture, sprinkle walnuts over, then fold in using a spatula.
3. Spoon mixture into a greased and lined 20 cm in square shallow cake tin. Smooth top using a spatula. Bake for 25-30 minutes, or until only just set. Cool in tin on a wire rack.
4. To make icing, combine chocolate and butter in a mixing bowl and beat until well blended. Spread over brownie and set aside to firm. Cut into squares to serve.