In a large mixing bowl, combine flour, sugar, baking powder, baking soda, and salt. In another bowl, whisk together buttermilk, milk, and the egg yolks. In yet a separate bowl, using an electric mixer, beat the egg whites until stiff peaks form.

Whisking constantly, add melted butter to the milk mixture. Pour the liquid ingredients into the bowl with the dry ingredients and whisk until just combined (do not overmix; a few lumps are okay.)

When the flour has been combined but the batter is still a little lumpy, heat a non-stick skillet or griddle to medium-low heat. While the skillet is heating, gently (but completely) fold beaten egg whites into the batter. When the skillet is hot, rub a stick of butter over the pan, or spray it with a little non-stick cooking spray and then ladle pancakes onto hot skillet. You can also put your batter in a pitcher to make pouring easier.

It takes a little adjusting to figure out where the temperature setting should be. When you start seeing bubbles, you're almost there. When the bubbles pop and leave a hole, it's time to flip. Gently slide a spatula under the pancake and quickly flip it to the other side. The other side won't take quite as long as the first side--just check here and there and when the pancakes are golden brown on both sides, you're good to go.