Open cans of pineapple, and drain liquid, (if using fresh, cut up fresh pineapple into small chunks). Place chunks into a ziplock bag and freeze for at least 2 hours, or overnight. Let thaw slightly just before making. (Do this by leaving it out on the counter for about 15 minutes, or microwave for about 30 seconds. You want to just be sure it is not rock solid frozen, so it can blend easily.)
Place pineapple and the rest of the ingredients in a food processor or powerful blender, and blend until smooth and creamy. *Note: You may need to stop the blender and help it along the blending process and/or add more milk if you blender is not very powerful.
Enjoy immediately or freezer for up to 20-30 minutes before serving!