In a medium bowl, combine the yeast and the warm water. Set the mixture aside for 15-20 minutes. Slowly add the all-purpose flour. Cover the mixture with a kitchen towel and let rise in a warm place for 1 hour.
In a separate bowl combine the buckwheat, egg yolks, butter, salt, sugar and milk. Add the mixture to the dough. Stir well blend. Cover and let rise for 1 hour.
Just before cooking, whip the egg whites until stiff. Fold into batter.
Heat a greased heavy griddle over medium high heat. Drop the batter on the griddle by the tablespoon, cooking each pancake until browned on both sides.