Crusty top banana muffins

I've got one very ripe bunch of bananas lying around which I don't wish for it to go to waste.

So I found a classic banana muffin recipe online....and 'cos RG likes a little crunch in his muffins and I do not have any nuts on hand, I decided to top the muffins with some crumble instead (similar to the topping on an apple crumble).

Ingredients:
1 1/2 cup of cake flour (you can use AP flour too)
1 tsp baking soda
1 tsp baking powder
1/3 tsp salt
3 ripe bananas (mashed with fork)
3/4 cup fine white sugar
1 egg
1/3 cup butter (melted in the microwave)
1/2 tsp vanilla essence

1/3 cup brown sugar
2 tbsp all-purpose flour
1/4 tsp ground cinnamon (more if you like stronger cinnamon taste)
1 tbsp butter (chopped)

Method:
Preheat oven to 375F. Line a 12-piece muffin tray with paper cups.
Mix together 1 1/2 cups of cake flour, baking soda, baking powder and salt in a bowl.
Use an electric mixer to beat together mashed bananas, white sugar, egg, melted butter and vanilla essence at high speed until well mixed.
Make a well in the flour mixture and pour in the banana mixture.
Use a mixing spoon to gently fold the ingredients together until even but do not over mixed.
Divide the batter into the 12 paper cups.
Meanwhile, mix together the brown sugar, 2 tbsp of flour and cinnamon and add in the chopped butter. Use your finger tips to rub in the butter until evenly mixed.
Sprinkle half the topping over the muffins and place the muffins in the oven to bake for about 15 minutes.
After 15 min, take out the muffins (without switching off the oven) and quickly sprinkle the remaining crumble mixture onto the muffins and then put the muffins back into the oven and bake for another 5 minutes or until a toothpick inserted into the centre of the muffin comes out clean.

[NOTE: Do not take too long to sprinkle the rest of the crumble onto the muffins. If not, the muffin centres might sink a little.]

The end product is a very soft and light textured muffin that's not too heavy to eat. And the crust gives a whole new dimension to the plain old banana muffin by adding a wonderful sweetness and crunch to every bite.