1 banana
2 tspn sugar
1 pint of milk

Put it all in a blender and blitz on the highest setting til it is all combined, the sugar has dissolved and it looks slightly thick.

Options: Add a raw egg if you like it really thick and frothy and don't mind taking the risk. Thats on your own head though as raw eggs can be bad for you.
The older and browner the banana the better, as long as its still ok to eat. Older bananas have more flavour and this is a good use for ones that you wouldn't normally eat because they're too soft. However you might want to use less sugar as old bananas are generally sweeter.

- Liam