Step 1: In a large bowl, whisk together the dry ingredients: flour, sugar, baking powder, baking soda, and salt. Ensure there are no lumps and the ingredients are well combined.
Step 2: In a separate medium bowl, whisk together the buttermilk, egg yolks, melted butter, and vanilla extract (if using) until thoroughly combined.
Step 3: In a clean, dry bowl, using an electric mixer or whisk, whip the egg whites until stiff peaks form. Be careful not to overbeat them.
Step 4: Pour the wet ingredients (buttermilk mixture) into the dry ingredients. Mix gently with a whisk or spatula until just combined. Do not overmix; a few lumps are fine.
Step 5: Gently fold the whipped egg whites into the batter in two additions using a spatula. Fold just until no streaks of white remain, being careful to preserve as much air as possible.
Step 6: Let the batter rest for 5-10 minutes. This allows the flour to fully hydrate and the leavening agents to begin their work.
Step 7: Heat a lightly greased griddle or large non-stick pan over medium-low heat. Test the heat by sprinkling a few drops of water; they should sizzle and evaporate within a few seconds.
Step 8: Pour approximately 1/4 cup of batter per pancake onto the hot griddle. Cook for 2-3 minutes per side, or until bubbles appear on the surface, the edges look set, and the bottom is golden brown. Flip carefully with a spatula and cook for another 1-2 minutes until golden brown and cooked through.
Step 9: Transfer cooked pancakes to a plate and keep warm in a low oven (around 200°F / 95°C) while you finish the rest of the batter. Serve immediately with your favorite toppings.