Whisk together the flour, sugar, baking powder, and salt in a large bowl; set aside. Whisk together buttermilk, eggs, vanilla, melted butter, and vegetable oil in a glass measuring cup. Whisk buttermilk mixture into flour mixture until just moistened (do not overmix; a few small lumps are fine). Gently fold in egg whites.
Heat a griddle or large nonstick skillet over medium heat. Use 1/2 teaspoon butter and 2 teaspoons oil to coat. For each pancake, ladle 1/3 cup batter 2 inches apart. Cook until bubbles form and pancakes are slightly dry around edges, about 3 minutes. Flip; cook until golden brown, about 3 minutes more. Repeat with remaining batter, adding butter and oil as needed. Serve with butter and syrup, if desired.