Preheat oven to 350 degrees F. Coat a 8-by-12-inch baking dish with cooking spray. Dust with a little flour, tapping out the excess, and set aside.Advertisement
Whisk together flour, cocoa and salt in a small bowl. Beat together brown sugar, oil, buttermilk, egg, egg whites and vanilla in a large bowl with an electric mixer on high speed until smooth, making sure no lumps of brown sugar remain. Add the dry ingredients and beat on low speed just until blended.
Transfer the batter to the prepared baking dish. Bake just until a knife inserted in the center comes out clean, 25 to 30 minutes.
Let cool in the baking dish on a rack. Cut into 15 bars. Store at room temperature in an airtight container.
2 other carbohydrate, 1 fat