Whisk together the flour, granulated sugar, baking powder, baking soda, and salt in a large bowl. In a separate microwave-safe bowl, melt the butter. Add the buttermilk and egg to the butter and whisk to combine. Add the wet ingredients to the dry ones and whisk to combine.
Heat a large nonstick skillet or a griddle over medium heat. Lightly grease the pan with butter. For each pancake, spoon a scant ⅓ cup of batter onto the prepared skillet and top with banana slices. Cook, turning once, until cooked through, 3 to 5 minutes. Repeat with remaining pancakes, buttering the skillet between batches if needed.
Serve topped with maple syrup.