Preheat oven: Preheat oven to 415°F (210°C). Line a 12-Muffin pan with muffin liners or grease thoroughly with butter if you don't have liners.
Dry ingredients: Sift flour into a large mixing bowl, add superfine sugar, brown sugar, and oat bran, mix well, make a well in the middle, and set aside.
Wet ingredients: In a second mixing bowl, using a fork, mash the banana until it's a smooth consistency. Then add melted butter, milk, and eggs and mix well.
Combine wet and dry ingredients: Pour wet ingredients into the well of the dry ones. Stir with a spatula or metal spoon just a few times.
Add chocolate chips: Continue to stir all ingredients until just combined, but don't over-mix. Remember that it's okay to have some lumps and some dry flour still showing in the batter; it's normal and a good sign for light and fluffy muffins.
Fill muffin liners: Fill the muffin liners with the batter until 2/3 full (around 2 – 3 scoops each); you can add some extra choc chips to the tops at this point if you like.
Bake: Bake the muffins for 18 minutes or until golden, or you can check with a skewer, insert it into the middle, and if it comes out clean, they're ready.
Allow to cool: Leave the muffins in the pan for 5 minutes to cool down slightly before removing them onto a cooling rack.