1. Put flour, sugar, baking powder, baking soda, and salt into a large bowl and whisk to combine; set aside. 2. Whisk together buttermilk, butter, vanilla, and eggs in a medium bowl. Pour the buttermilk mixture into the flour mixture and whisk together until just combined to make a thick batter. (For tenderer flapjacks, don't overmix the batter.) 3. Heat an 8" nonstick skillet over medium heat. Add 1 tbsp. butter and heat until the butter's foam subsides. Ladle in about 1/2 cup of the batter. Cook the flapjack, turning once, until deep golden brown on both sides, about 5 minutes total. Transfer to a large plate; keep warm. Repeat process with additional butter and remaining batter to make 8 flapjacks in all. Serve hot, topped with butter and maple syrup and a dusting of confectioners' sugar.