Method

Mash the ripe bananas in a bowl, then mix in the egg, melted butter and vanilla until smooth. In a separate bowl, combine the flour, sugar, baking powder, baking soda and salt. Fold the dry mixture gently into the banana mixture to form a soft batter. Spoon the batter into muffin cups. For the crumble topping, rub the flour, sugar and cold butter together with your fingertips until crumbly, then sprinkle the mixture evenly over each muffin. Bake in a preheated oven at 180°C for 18–22 minutes, or until the muffins rise and become golden with a crisp crumble top.