Heat the oven to 450°F. Set 4 shallow (4 oz.) ramekins on a baking sheet. In a large bowl whisk together the flour and 3 tablespoons of the sugar. Gradually whisk in the milk and the heavy cream until a smooth paste forms. Whisk in the egg, egg yolk, vanilla, and salt.
Melt the butter in a 10-inch skillet over medium-high heat. Add the remaining sugar and swirl the pan to combine. Cook until the mixture just begins to caramelize, 1 to 2 minutes. Decrease the heat to medium, carefully add the bananas, and stir gently to combine. Cook 1 minute more, until the bananas are warmed and coated in the sauce. Remove from the heat and divide the banana mixture among the ramekins. Pour in the milk mixture, dividing evenly between the ramekins.
Bake until the edges are puffed, the tops are golden, and the centers are set and no longer runny, about 15 to 18 minutes. Let cool slightly, then sprinkle with confectioners’ sugar. Serve warm.