Brownie: Melt 250g butter in a large saucepan. Add 2 cups light brown sugar and beat well to mix. Cool the mixture slightly then beat in eggs and vanilla.
Sift together plain flour, salt and baking powder. Stir it into the wet ingredients then add the nuts. Mix well.
Spread batter in a greased 30 x 15 x 3cm pan and bake for 30-35 minutes or until a light gold. Cool in the pan for 10 minutes, then turn out of pan and let brownies finish cooling on a rack.
Coffee Icing: Disolve coffee in the water. Cream 125g butter with icing sugar. Beat it until light. Beat coffee into the sugar mixture. Spread over the brownies. When icing has set, cut brownies into squares.