Add the flour, club soda, milk, powdered sugar, cornstarch, vanilla and salt to a medium-sized bowl. Whisk to combine and break up any lumps. Add the sliced bananas and stir them around to coat them completely in the batter. Cover the bowl and refrigerate while you make the chocolate fondue and heat the oil for the bananas.
For Frying: Add about 1-inch of oil to a Dutch oven or heavy bottomed skillet. Attach a candy thermometer and bring the heat up to 350 degrees F. Once the oil is hot, remove the bananas from the fridge, letting any excess batter drip back into the bowl, and transfer them to the oil. Fry until golden brown, 1 to 2 minutes per side. Use a slotted spoon to remove the bananas to a wire rack. Let the bananas cool for 1 minute. Dust with powdered sugar and serve immediately with the Chocolate Fondue and other dippers using fondue forks of wooden skewers.
Add the chocolate, heavy cream and vanilla to a large bowl set over a double boiler. Heat over medium-low, stirring occasionally, until the chocolate is completely melted and incorporated with the cream, about 5 minutes. Keep warm on the double boiler until ready to serve. Once ready to serve, carefully transfer the chocolate fondue to a fondue pot to keep warm.