Preheat the oven to 200 degrees C and spray muffin trays with cooking oil or grease them.

Put (or probably best to sift) into a bowl - Flour, baking powder and sugar.  Stir in the chocolate chips and weetbix.  Make a hole in the middle of the mixture.   Beat the egg and stir in the butter (melted) and milk, then pour this liquid into the dry ingredients. 

Add banana then stir, but only until it's just all mushed together.  Fill muffin trays and cook for 15-20 mins @ 200 degrees or until your metal stick comes out clean.

Bang the bottom of the trays and empty them onto a cooling rack, then try and eat them before anyone else works out what you've been doing.  The smell is a bit of a giveaway though.

Unintentional variation - I've found if you leave the baking powder out you get quite an intense banana choc rock cake type experience - not fantastic,  but worth a go for something different I guess especially if there's no baking powder in the pantry.