A number of different chefs have done something like this, but here's my take.
Take 2 overripe bananas per serving and peel them and cut them into slices that are 1/2 inch wide. Freeze them in a flat layer until they are solid, a good 6 hours at least. Right before serving, puree the bananas in the food processor (not more than 6 or so at a time). If the bananas are having a tough time pureeing, you can add some milk to help it get going. Top it however you like, I especially like a quick mix of honey and peanut butter and some chocolate. Hard freeze any leftovers and they will stay good.