1. Combine the flour, baking powder, and salt in a medium mixing bowl.
2. Whisk together yogurt, milk, and water. Add the melted butter (and vanilla, if using) to the milk mixture and stir to combine.
3. In a clean metal or glass bowl, beat the egg whites with a mixer until soft peaks form (2-3 minutes).
4. Combine the dry and liquid mixtures together. Add half the beaten whites and stir gently to combine, then add the remaining whites and fold gently into the batter, preserving as much air as possible. Allow to stand until bubbling (2-3 minutes).
5. Heat a griddle over medium-high heat. Ladle about 2 tablespoons of batter onto the pan to form a 4? pancake. Cook until center is bubbly and edges are dry (1 and a half minute). Flip and continue to cook until the center is done (30-45 seconds). Remove to a plate in a just-warm oven and repeat this step until batter is gone.
6. Serve hot, topped with fruit.