Preheat oven to 400°. In a large cast-iron or other heavy skillet, melt butter over medium heat. Stir in brown sugar until blended. Add bananas; stir to coat. Remove from heat; set aside., Unfold puff pastry; cut into 4 rectangles. Place a halved banana in center of each square. Overlap 2 opposite corners of pastry over banana; pinch tightly to seal. Place on parchment-lined baking sheets. , Bake until golden brown, 20-25 minutes. Drizzle with chocolate. Serve warm, with ice cream if desired.