In a large skillet melt the butter over medium heat.
Whip the egg whites with a pinch of salt to very stiff peaks and refrigerate.
In a bowl, stir together the yolks, ricotta and milk. Remove the egg whites from the refrigerator.
Stir together the flour and baking powder and sprinkle them over the egg whites. Fold the mixture into the ricotta mixture. Spoon a large tablespoon of batter into the pan. Saute over medium heat until the underside is golden brown, about 2 minutes. Gently flip the pancake over and cook until golden brown. Repeat with the remaining batter. Sprinkle with powdered sugar before serving.