A very good, very chocolaty cookie which is crisp outside and chewy inside.
Preheat the oven. Line a baking sheet with baking parchment. Using an electric beater, whisk the egg whites until frothy. Add the sugar, cocoa, flour, coffee and water to the bowl and beat first at a slow speed to blend the ingredients and then at a higher speed for a few minutes until the mixture thickens. Fold in the walnuts. Place tablespoons of the mixture on the prepared baking sheet leavi