In a medium bowl, whisk together the flour, sugar, baking powder and salt. In another bowl, whisk together the milk, egg yolks and melted butter. Pour the wet mixture into the dry and stir until just combined.
Preheat a griddle or large nonstick skillet over medium heat. Meanwhile, beat the egg whites to soft peaks. Gently fold the whites into the batter.
Grease the griddle and ladle on 1/4-cup portions of batter. Cook on 1 side until bubbles form and the pancakes are cooked around the edges, 1 1/2 to 2 minutes. Flip and cook through, 1 minute more. Serve with butter and maple syrup.