In a mixing bowl, combine the melted butter or margarine with the sugar. Add the vanilla and egg and beat for 2 minutes. Add the mashed banana until combined.
In a separate bowl, combine the flour, baking soda, baking powder and salt. Slowly add to the mixing bowl just until combined. By hand, stir in the milk.
Heat a griddle or skillet over medium heat. Grease well. Use about 2 T. batter for each pancake. They will spread considerably. Cook about 5 -6 minutes, flip and cook an additional 3 minutes. Grease the griddle or skillet well in between each batch.