In a small bowl, whisk together flour, sugar, baking powder, baking soda, and salt.
In a medium bowl, whisk together buttermilk, egg yolk, butter, and vanilla. Add flour mixture and stir until just combined--batter will look a little thick.
Heat griddle to 350°F or skillet to medium heat.
While your griddle heats, in a small bowl, with a handheld electric mixer, beat egg white on high until stiff peaks form--the egg should be bright white, and when beaters are lifted out, peaks should stand straight up.
Fold egg white into the batter with a baking spatula, being careful not to overmix and deflate the egg.
Once your cooking surface is hot, lightly grease, and drop on slightly heaping 1/3 cups full of batter (if making in a skillet, you will have to cook in two batches) and cook until bubbles begin to form on the surface of your pancakes. Flip and cook until done.
Add your favorite toppings and enjoy!