In a small bowl, mash banana and peanut butter together, using a fork, until mixture is creamy with small pieces of banana.
Spread one side of each of piece of bread with soft (room temp) butter. Place two pieces of bread, butter side down in a skillet (on medium heat).
Remove sandwich to serving plate. Cut diagonally, and serve! Can garnish sandwich with sliced bananas, if desired.
Grilled "Elvis Special" Sandwich https://www.thegratefulgirlcooks.com/grilled-elvis-special-sandwich/