In a very large bowl or stockpot (one that can comfortably hold 36 cups of batter), whisk together the flour, sugar, baking powder, baking soda, and salt., In a separate large bowl, whisk together the eggs, buttermilk, milk, butter, and vanilla., Pour the wet ingredients into the dry ingredients, stirring to combine. Stir until the mixture is fairly smooth; some small lumps are OK. Allow the batter to rest, uncovered, for 15 minutes., Spoon batter in 1/4-cupfuls onto a preheated 325°F to 350°F griddle. Cook until bubbles form on the tops of the pancakes and the bottoms are brown. Flip, and cook until the bottoms are brown. Serve immediately, or hold briefly in a warm oven.