Heat the coconut oil in a fry pan over medium heat. Add the bananas, flat side down, and cook for about 3 minutes or until golden. Flip the bananas and cook for another 3 minutes or until golden. Don't worry if the bananas fall apart; they'll be puréed anyway. Remove pan from heat and let cool for several minutes.
Scoop the contents of the fry pan into a container, scraping off all the caramelized bits stuck to the pan, and put the container in the freezer.
Once the bananas are frozen, place in a food processor or blender with the milk and peanut butter, if using, and purée until smooth and creamy. Scoop everything back into the container and freeze.
When ready to serve, let ice cream sit at room temperature for 5-10 minutes so it's easier to scoop.
Notes
You can use any type of unflavored or flavored milk you prefer, including almond milk, rice milk, coconut milk, etc.
Recipe by Two of a Kind at http://www.twoofakindcooks.com/caramelized-banana-ice-cream/