Preheat oven to 175 degrees. Whisk flour, sugar, baking powder, and salt in a medium bowl. Add egg, milk, and butter; whisk until combined but still slightly lumpy.
Heat a large nonstick skillet over medium heat. Place 5 banana rounds in pan, about 3 inches apart. Spoon one tablespoon batter over each; cook until large bubbles cover surface, 1 to 2 minutes. Flip, and cook until bottom is golden, about 1 minute more. Transfer to a baking sheet, and keep warm in the oven.
Repeat with remaining banana rounds and batter. Saute extra banana slices in butter until golden; serve with pancakes.