In an electric mixer, cream together the butter, brown sugar and cocoa powder.
In a small bowl stir together the water and instant coffee granules until the crystals dissolve.
Add the dissolved coffee, egg whites and yogurt to the mixer and beat until it is smooth and creamy.
Slowly add the flour. The cookie dough will resemble a cake batter when done.
Drop a tablespoon sized amount of batter in the bowl of sugar. Lightly coat the dough in the sugar roll it in your hands to make an even ball. Drop the ball of dough back into the sugar and coat it a second time.
Place the balls 2 inches apart on a cookie sheet lined with parchment paper. Bake in a 350F oven for 8-10 minutes. Let them cool on a wire rack.