Cut 2 bananas into 1/4-inch-thick rounds. Combine 1/4 cup melted butter, 1/2 cup sugar, and 1/4 cup water in heavy large skillet. Boil over medium-high heat until mixture thickens slightly, about 2 minutes. Stir in vanilla extract and sliced bananas. Remove syrup from heat.
Whisk flour and remaining 1/4 cup sugar in large bowl. Mash remaining banana in medium bowl, then whisk in buttermilk and eggs. Stir banana mixture into dry ingredients (some lumps will remain). Mix in remaining 1/4 cup melted butter.
Preheat oven to 200°F. Heat griddle over medium heat; brush with additional melted butter. Working in batches, pour batter by 1/3 cupfuls onto griddle. Cook pancakes until golden, about 2 minutes per side. Transfer pancakes to baking sheet; place in oven to keep warm.