Pre-heat the oven to 180 ºC (350 ºF) and line a cupcake tray with 9 cupcake cases.
Bake in the pre-heated oven at 180 ºC (350 ºF) for 20 – 23 minutes, or until the crumble is light golden brown and an inserted toothpick comes out clean.
Note 1: How much sugar you use depends solely on how sweet you want your muffins to be. I prefer the lower end on the sweetness range, but tastes differ. Using the full amount of sugar gives a more dessert-like muffin.