Preheat oven to 350 degrees. Line baking sheets with parchment paper or spray with nonstick cooking spray.
Whisk together sugar, prune puree, yogurt, oil and egg whites. In a separate bowl stir together flour, cocoa, salt, soda and coffee. Blend the dry ingredients into the wet ones. Drop the dough by spoonfuls onto the baking sheets. Bake 12 to 14 minutes.