Buttermilk substitute: 2/3 cup yogurt whisked together with 1/3 cup milk
Combine flour, baking powder, baking soda, salt, and sugar in a medium bowl and whisk until homogenous.
In a medium clean bowl, whisk the egg whites until stiff peaks form.
In a large bowl, whisk the egg yolks, buttermilk, and sour cream until homogenous.
Slowly drizzle in the melted butter while whisking.
Carefully fold in the egg whites with a rubber spatula until just combined.
Pour the mixture over the dry mix and fold until just combined (there should still be plenty of lumps).
Heat a large heavy-bottomed nonstick skillet over medium heat for 5 minutes (or use an electric griddle). Add a small amount of butter or oil to the griddle and spread with a paper towel until no visible butter or oil remains.
Use a 1⁄4-cup dry measure to place 4 pancakes in the skillet and cook until bubbles start to appear on top and the bottoms are golden brown, about 2 minutes.
Carefully flip the pancakes and cook on the second side until golden brown and completely set, about 2 minutes longer.
Original Recipe on Serious Eats