Sift together flour, salt, baking soda and powder. Add buttermilk, egg yolks and butter, stir until smooth. Beat whites until soft peaks form. Fold into batter. Heat Aebelskiver pan over med-low heat. Butter each cup and the top surface. Pour batter into each cup and cook until bubbles form in the center of the liquid batter. Flip over using a skewer or the tine of a fork. Cook until ball is golden brown on all sides. Keep warm in the oven until all are cooked. Sprinkle with powdered sugar and serve with warmed applesauce.