Preheat oven to 200 C / Gas 6. In a bowl combine milk and cereal; set aside. In a separate bowl sift together the flour, baking powder and salt; set aside.
In the bowl of a food processor (or a large mixing bowl if you prefer to mix by hand), cream together the brown sugar and egg on high speed. Add vanilla and banana and stir until mixture is smooth, then add cereal mixture.
Add raisins, chocolate chips, then the melted butter or margarine; finally, add flour mixture all at once and mix until everything is moist. Do not overmix to ensure fluffy, well-risen muffins!
Spoon mixture into greased muffin tins or cases, filling each about 2/3 full.