Preheat oven to 350 degrees. Grease a 9 by 13 inch baking pan and set aside. In a mixing bowl, combine flour and sugar. Cut in butter until crumbly. Set aside 3/4 cup for topping. Add the baking powder, milk and egg yolks to remaining mixture; mix well.
Beat egg whites until soft peaks form. Gently fold egg whites into batter. Pour into a greased baking dish. Sprinkle with blueberries and reserved crumb mixture.
Bake at 350 degrees for 30-35 minutes or until golden brown and a toothpick inserted near the center comes out clean.