Lightly spoon barley flour and wheat flour into dry measuring cups; level with a knife.
Combine barley flour, wheat flour, and next 5 ingredients (through salt) in a large bowl; stir with a whisk.
Combine buttermilk, maple syrup, butter, and egg yolks in a bowl; stir with a whisk.
Add buttermilk mixture to flour mixture, stirring until combined.
Beat egg whites with an electric mixer at high speed until stiff peaks form (do not overbeat). Fold egg whites into batter. Spoon about 1/3 cup batter onto a hot nonstick griddle or nonstick skillet coated with cooking spray. Turn flapjacks when tops are covered with bubbles and edges are cooked.
