Spread bread slices with peanut butter. Top 4 bread slices with bananas and remaining bread slices, peanut butter sides down, pressing firmly. Cut sandwiches into 1-inch pieces; place in 8 lightly greased (8-oz.) ramekins.
Whisk together eggs and sugars; whisk in whipping cream. Gradually pour mixture over sandwich pieces in ramekins.
For Streusel: Stir together flour and brown sugar in a bowl. Cut in butter and peanut butter with pastry blender or fork until mixture resembles small peas. Stir in peanuts.
Sprinkle Streusel on top of sandwiches in ramekins. Place ramekins in a 15- x 10-inch jelly-roll pan. Cover and chill 2 to 24 hours.
For Caramel Sauce: Cook sugar in a 3-qt. heavy saucepan over medium heat 6 to 8 minutes or until sugar caramelizes, tilting and swirling pan to incorporate mixture. Stir in whipping cream. (Mixture will bubble and harden.) Cook, stirring constantly, until mixture melts and begins to boil (about 5 minutes). Quickly pour sauce into a bowl; stir in vanilla, and salt. Let cool 15 minutes. Serve warm or cool.
Note: To make ahead, cover and chill up to 3 weeks. To reheat, cook, uncovered, in a microwave-safe glass bowl at MEDIUM LOW (30% power) for 2 minutes or until warm, stirring once.
Preheat oven to 375°. Let puddings stand at room temperature 30 minutes. Bake 20 to 25 minutes or until golden brown, set, and puffed. Serve warm with Dark Caramel Sauce. Garnish, if desired.