- 3/4 - cup all-purpose flour
- 3/4 - cup whole-wheat pastry flour
- 3 - tablespoons unsweetened cocoa powder
- 1/2 - teaspoon baking soda
- 1/2 - teaspoon salt
- 6 - large egg whites
- 3/4 - cup granulated sugar
- 1 1/2 - cups packed dark brown sugar
- 1 - tablespoon vanilla extract
- 3 - ounces unsweetened chocolate
Position rack in the center of the oven; preheat to 350° F. Line a large baking sheet with parchment paper or a silicone baking mat.
Whisk all-purpose flour, whole-wheat flour, cocoa powder, baking soda and salt in a medium bowl. Beat egg whites in a large bowl with an electric mixer until foamy, about 1 minute. Beat in granulated sugar in a slow, steady stream. Scrape down the sides, then beat in brown sugar 1 tablespoon at a time. Beat until smooth, about 3 minutes. Beat in vanilla and melted chocolate. Stir in the dry ingredients with a wooden spoon until just incorporated.
Drop the batter by tablespoonfuls onto the prepared baking sheet, 1 1/2 inches apart.
Bake the cookies until flat yet springy, with slightly cracked tops, 10 to 12 minutes. Cool on the pan for 5 minutes, then transfer to a wire rack to cool completely. Let the pan cool for a few minutes before baking another batch; replace parchment paper if torn or scorched.