16 ounces (1 pound) frozen pineapple pieces
1 recipe Marshmallow Creme (or 1 14-ounce tub of store-bought marshmallow fluff)
Divide the pineapple pieces into two equal portions. Leave one portion frozen, and defrost the other portion either by allowing it to sit at room temperature or by placing it in the microwave on low power until just cold, but not frozen. Place the defrosted portion of pineapple pieces into a blender or food processor and process until smooth. Add about 1/4 cup of the marshmallow creme, and the frozen portion to the blender or food processor. Process until the pineapple pieces are smooth. If necessary to keep the machine moving and blending, add more marshmallow creme slowly.
Transfer the pineapple mixture to a large bowl, add the remaining marshmallow creme and mix to combine. The mixture will go from dark yellow in color to light yellow, and it will be relatively thin. Do not overmix.
For a scoopable consistency, transfer the mixture to a freezer-safe container with a tight fitting lid and place in the freezer for at least 6 hours or overnight. If frozen for longer than 12 hours, leave the container out on the counter for 10 minutes for it to reach a scoopable consistency.
For a soft serve consistency, transfer the mixture to a large disposable piping bag fitted with an open piping tip, leaving the tip of the bag closed. Close the top of the piping bag with a clip or rubber band. Place the piping bag upright it in the freezer for about 4 hours or until mostly firm. Snip off the end of the bag, pipe into bowls and serve immediately. It will melt quickly, like proper soft serve ice cream.