Melt the butter. Whisk the dry ingredients together in a large bowl. In a medium bowl, whisk the 2 egg yolks and the buttermilk until combined. Make a well in the center of the dry ingredients, pour in the liquid mixture, and stir until just barely mixed. Add the melted butter and mix until just combined.
In a medium bowl using an electric mixer, whip the egg white until soft peaks form. Fold into the batter.
Ladle ¼ cup (for smallish pancakes) to ½ cup (for large pancakes) of the batter onto a preheated griddle or non-stick pan. Cook until bubbles appear on the surface and the underside of the pancakes are golden brown, about 2-4 minutes. Turn them over and cook until done, about 2-4 minutes longer.