Just heavy cream whipped with some sugar-free flavouring. Sometimes I'll add an egg yolk, it won't get as fluffy, but makes it harder to end up overwhipping and ending up in butter territory. Usually something like mio or sugar-free koolaid drops, but sometimes some instant coffee or cocoa powder with splenda. I bought some licorice (anise) flavouring at Walmart once when it was on sale for a dollar, that was really good. I would have emptied the shelves if I'd known they were going to stop selling the stuff at any price once they ran out.