Peel banana and slice into chunks. Place in an airtight, freezer-friendly container and freeze for 6 hours or overnight, or all day, what have you, until banana is frozen solid.
Spoon frozen banana slices into a blender or food processor. Bash together until smooth and the consistency of soft-serve ice cream. This can range from 4 to 8 minutes, depending on your blender or food processor. Add the almond milk. Blitz briefly again.
Enjoy at once or freeze again until you're ready. Whip again before serving for optimal creaminess.