Place 2 pieces of white bread in the toaster on a light setting. Heat skillet over medium heat with 2 tablespoons butter. While the bread is toasting, in a small bowl, using a fork mash the ripe banana until it reaches a smooth consistency. Using a knife, take both pieces of the toasted bread and spread 2 tablespoons of creamy peanut butter, topping 1 side with the mashed banana. Place 1 slice of bread on top of the other forming a sandwich. Place sandwich in hot skillet browning each side, flipping with a spatula, about 2 minutes per side. Take out of skillet, slice on a diagonal and serve on a plate.