It sounds like a brain teaser: How can you make ice cream with only one ingredient? Maybe freeze milk? Nope, doesn't work. How about, um, er.... Give up? The single ingredient is a banana. And once you taste it, you're going to kick yourself for not thinking of this before.
You could stop there or you could add some ingredients. Here's a favorite:
Take two frozen bananas and given them a rough chop in the food processor or even a blender. Add one tablespoon of defatted peanut butter like PB2 or any natural nut butter, like almond butter. Add one scoop of chocolate or vanilla Metabolic Drive® Protein. Stir or blend lightly. Add a splash of almond milk if needed. Eat with a spoon.