In a large bowl, combine flour, baking powder, and salt.
In a separate bowl, whisk mashed banana, butter, egg, buttermilk, brown sugar, and vanilla. Add the wet ingredients to the dry and stir with a rubber spatula until combined, being careful not to overmix.
Heat a griddle or large skillet over medium-low heat and grease with butter. Drop the batter in approximately 1/3 cup portions onto the griddle, spreading out the batter to form even circles. Cook until bubbles begin to form (it might be hard to see the bubbles because the batter will be thick). Flip and continue cooking until cooked through (another couple minutes). Be careful not to turn up the heat too high, as you want the pancakes to cook slowly so that the outside doesn't cook faster than the inside. Serve hot with butter and syrup.
