Preheat oven to 350°. Place the egg whites, cottage cheese and vanilla in a blender; cover and process until smooth. Add chocolate; cover and process just until blended, about 15 seconds. Combine the sugar, flour, baking powder and salt; add to cottage cheese mixture. Cover and pulse until just moistened.
Spread into an 8-in. square baking pan coated with cooking spray. Bake until a toothpick inserted in the center comes out clean, 20-25 minutes (do not overbake). Cool on a wire rack. Dust with confectioners' sugar. Cut into bars.