Melt the butter and chocolate in a pan on a low heat. Remove the pan from the heat, stir in the sugar. Add the eggs and salt to the mixture. Dissolve the coffee powder in the water and stir in. Add the cashew nuts and flour. Transfer the cake mixture to the prepared tin.
Bake for approx. 25 mins. in the lower half of an oven preheated to 180°C. The brownies should still be a little gooey inside. Remove the brownies, allow to cool a little, cut into squares while still warm, transfer to a cooling rack along with the baking paper, leave to cool. Separate the brownies from the baking paper and place on the rack, place the rack on a sheet of baking paper.
Mix the icing sugar and espresso, pour over the brownies.