1. Whisk flour, sugar, baking soda, and salt together in a large bowl. 2. Stir the buttermilk and sour cream together in a medium bowl until combined. Add the 2 egg yolk and butter to the buttermilk mixture and stir well to combine. 3. Whisk all 4 egg whites in a clean bowl to soft peaks. 4. Pour the buttermilk mixture over the dry ingredients and whisk just until combined. Lumps and visible streaks of flour are good. Using a spatula, carefully fold the whites into the batter just until combined. Do not overmix; a few streaks of whites should be visible. 5. Heat about 1 tablespoon oil in a large nonstick skillet over medium low heat for 5 minutes. Ladle 2 tablespoons (1/8 cup) batter into the pan. Cook until the bottoms are evenly browned, 2 to 3 minutes. Flp and cook until golden brown on second side, 2 to 3 minutes longer.