Two bananas does about 1 good serving plus extra for picking
Peel your bananas and chop them into discs. Pop them on a plate and bung them in the freezer. Leave until they are frozen solid - I tend to put them in before I go to bed and have it at some pointthe following day.
When the banana is frozen, take it out and put the discs in a blender - note: you may find it difficult getting them off the plate so I suggest using a fork or something to chisel them off!
Blend until super smooth. You'll need to stop the blender and push it all down a bit with a fork at the start but then it should turn nice and smooth.