Preheat your oven to 350ºF (180ºC) and line a 12 hole muffin tin with cupcake wrappers.
In a stand mixer or large bowl, cream your butter and sugars together until light and fluffy.
Peel the bananas and add them into the butter/sugar mixture. If they're very ripe they should mush up really easily.
Crack the eggs into a jug and gently whisk before adding to the mixture, along with the milk and vanilla extract. It won't look very attractive as it'll be lumpy from the bananas, but that's OK. It comes good!
Add the flour, baking soda, baking powder, cinnamon and mixed spice to the batter and fold in gently, until just mixed. Be careful not to overmix as your muffins may go tough.
Chuck in your chocolate chips, and stir gently until well distributed.
Using an ice cream scoop, add a level scoop of muffin mix into each of the liners and bake for 18-20 minutes, until a skewer comes out clean.
Remove from the heat and put the muffins on a cooling rack to chill.