Add the frozen pineapple, ice cream, and ½ cup pineapple juice to a blender and blend until smooth. Add the remaining pineapple juice, as needed, to reach your desired consistency.

Transfer to a piping bag fitted with a star tip and pipe into 2 cups, or scoop into the cups.

Serve immediately or freeze. If desired, you can serve with extra pineapple juice on top for a float-style treat.