In a large bowl, sift together, flour, sugar, baking powder, baking soda, and salt. Set aside. In a smaller bowl whisk together vanilla, buttermilk, yogurt, eggs, and melted butter. Gently fold the wet ingredients into the dry until just combined and no large lumps are visible. Do not overmix. Let the batter rest for at least 15 minutes. The batter can be made overnight.