If necessary, peel the bananas, then cut them into coins. Place the bananas in a blender or food processor and blend until creamy.
Notes
Add a splash of water - You may need to add a splash of water or milk or non-dairy milk to the blender if the bananas are pretty frozen and not blending up quickly.
Defrost them a bit - I like to set my frozen bananas on the counter for about 15 minutes before blending them so that they are not rock hard. It also makes it easier to slice the bananas if I've frozen them whole. Make sure they don't get too soft, though - you want them to be firmly frozen when you add them to the food processor.
Keep bananas in the freezer - I always have a bag of bananas in the freezer because we don't always eat up our ripe bananas as quickly as I anticipate. Rather than waste them, I pop the whole, unpeeled bananas into a freezer-safe bag and keep them in the freezer for baking and ice cream. You can also peel your bananas or cut them into coins - you do you - but I leave them whole and unpeeled to keep things easy.
Make sure to cut the bananas - Roughly chop or cut the frozen bananas into pieces before adding them to the blender or food processor.
Food processor vs. blender: You can use a high-powered blender or food processor to make this banana ice cream. I prefer the food processor because it's strong enough to break down the bananas, and there's plenty of room for the bananas to puree. If you do use a blender, make sure it is strong enough to fully puree the bananas.
Double the batch - Go ahead and double or even triple your batch of banana ice cream.