Cut the banana into thin slices, and place on a baking tray freeze for one hour.
Remove banana from the freezer. Pour the cold water or unsweetened almond milk into a blender and add the banana.
Using a wooden spoon, break up the frozen raspberries into small pieces and add to the blender. Blend on high setting for 3-4 minutes. Add more liquid if the blades jam or leave for 5 minutes for the mixture to soften up, then continue to blend until smooth.
Add honey, yogurt and peppermint extract (if using) and pulse until creamy.