Preheat the oven to 350 degrees F. Spray four 10-ounce mini cast-iron skillets with baking spray.
Place the muffin cubes in a large bowl. Combine the milk, sugar and eggs in a separate large bowl. Stir until the sugar partially dissolves, about 3 minutes. Add the melted butter and stir to mix. Pour the mixture over the muffin cubes and toss. Divide among the prepared skillets. Bake until the custard is set but still a little wobbly and the edges of the muffin cubes have browned, 30 to 35 minutes. Pour the melted cream cheese frosting over the bread pudding and scatter with the banana chips.