Combine pineapple juice, sugar and amaretto until sugar has dissolved. Pour into two ice cube trays and freeze until firm, about 6 hours.
Add frozen pineapple juice cubes to the blender pitcher and secure the lid.
Touch CRUSHED ICE, then touch START. Use the tamper to push cubes towards the blades. Repeat the program if needed.
Serve immediately for soft-serve. For a firmer product, spread evenly into a flat-bottomed container, press plastic wrap against the surface of the sorbet and freeze 4+ hours.