Put the bananas in a large bowl and mash with the back of a fork until you have a smooth puree. Add the peanut butter, butter and maple syrup and mix well to combine (unless they are really cold, the action of mixing should be enough to melt them and allow them to mix).

Sprinkle the mixed spice and cinnamon in, then add the oats and mix well to combine. Taste test if you wish and add more spice or a bit of extra sweetener if desired. (If adding in any extras such as raisins, nuts, chocolate chips, add them at this stage).

Tip into a lined, greased or silicon tin and flatten out with the back of your spoon until the mix is equally distributed.

Using a fine grater, grate your chocolate directly over the tin, aiming to cover as much as the mix as possible.

Bake at Gas Mark 4 (350f / 180c) for 30 minutes. The bars should be slightly pulling away from the edge of the tin. Leave in the tin to cool for 10 minutes, before turning out to cool on a wire rack.

Slice into bars. Enjoy!