Cut the peeled bananas in 2 lengthwise. Sprinkle them with lemon juice, rum and sugar and let them stand for half an hour.
Mix the flour, starch, vanilla, oil, egg and milk together and leave this crumbing in the refrigerator for 30 minutes. Before frying the bananas, drain the bananas, roll them in the crumbing well and fry them in preheated oil.
Drain them on a cooking grid and serve sprinkled with powdered sugar.