Heat oven to 170C/150C fan/gas mark 3. Line muffin tins with 16 cases.
In a bowl, combine the flour, sugar, 1⁄2 tsp salt and bicarbonate of soda. In another bowl mix the mayonnaise, mashed bananas and vanilla extract.
Pour the wet ingredients into the dry and mix with a spoon until just combined (don’t overmix or your cupcakes will be heavy). Spoon the mixture into the cases and bake for 20 mins.
Leave in the tray for 5 minutes then move to a cooling rack.