Preheat oven to 180C, 350F, gas mark 4. Grease
8 inch square cake tin with butter and line with baking
paper. Place the chocolate and butter in a small heatproof
bowl and set over a saucepan of gentle simmering water
until melted. Stir until smooth. Remove from the heat
and leave to cool. Beat the sugar and eggs together
until pale and thick. Fold in the chocolate mixture
and coffee. Mix well. Sift the flour, baking powder
and salt into the mixture and fold in. Fold in the walnuts.
Pour into tin and bake for 20-25 minutes. Leave to cool before serving the Chocolate Mocha Brownies.