Place bacon slices on baking sheet pan with sides (jelly roll pan) and bake until lightly browned and starting to crisp, about 5-6 minutes. Meanwhile, mix brown sugar and maple syrup until smooth. Brush hot bacon slices with mixture, using a pastry brush. Return to oven for another 5-6 minutes, turning once and being careful not to burn sugar. Remove to cooling rack and let cool.
Heat griddle or sauté pan over medium heat. Butter one side of bread slices. Spread other side with peanut butter. Top each slice, peanut butter-side up, with 1 Butterkäse slice and some banana slices. Place butter-side down on griddle and grill until sandwich bread bottoms are light golden brown. Meanwhile, heat chocolate sauce until warm. Dip each slice of bacon into warm chocolate to cover half of strip and place over bananas. To serve, drizzle sandwiches with additional chocolate sauce.