There are many variations to this recipe; you can use water or plant based milk. I've always made mine with cold water from the refrigerator. You could use the frozen banana alone or add other frozen fruits and or nuts.
Ingredients for above pic.
1 sliced, frozen banana
1/2 cup frozen mango
handful of blueberries - fresh or frozen
1/2 cup cold water or plant based milk
Add ingredients to blender, blend until thick and creamy. Pour into a glass and enjoy!