How to Make It
In a medium saucepan, combine the butter with the cream, brown sugar, rum, Grand Marnier, ginger and vanilla bean and seeds. Cook over moderately high heat until thickened, about 5 minutes. Strain the sauce into a bowl and keep warm.
Peel and halve the bananas crosswise and cut each piece lengthwise three-quarters of the way through. Stuff each banana with a piece of chocolate.
In a large pot, heat 2 inches of vegetable oil to 350°. Put 1/4 cup of the cake flour in a shallow bowl. In a medium bowl, mix the remaining 1 1/2 cups of cake flour with the cornstarch, baking powder and salt. Stir in the club soda just until incorporated; the tempura batter will be lumpy.
Dust each stuffed banana with the cake flour in the bowl, then coat with the tempura batter. Carefully add the bananas to the oil and fry, turning a few times, until lightly golden, about 3 minutes. Using a slotted spoon, transfer the bananas to paper towels to drain. To serve, arrange the banana halves in shallow bowls with a scoop of vanilla ice cream and top with the caramel sauce.