Heat oven to 350°F. Spray cookie sheets with nonstick cooking spray or line with parchment paper. In a large bowl of a food processor or a large bowl, combine the flour, sugar, brown sugar, cocoa, baking powder and salt, breaking up any lumps of brown sugar. Add the butter and pulse or stir with a fork, pastry cutter or whisk until the mixture is well combined and crumbly. If using food processor, spoon flour mixture into large bowl.