Add water to a heavy-duty pot, attach your immersion cooker and heat water bath to 35ºC/95ºF.
Add the whipping cream and buttermilk or coconut cream and citrus juice to a canning jar, seal and add to heated water. Cook for 8-12 hours. (I usually check the consistency around the eighth hour and continue cooking up to 12 hours, if needed)
Remove from water bath when time is up and place on a towel on a counter to cool. While cooling, prepare a water bath (ice and cold water) and submerge the jar to cool further. If cooking in a bag, transfer to the ice bath immediately, as there is no risk of a jar cracking. Transfer to the refrigerator overnight. Enjoy! (this will keep for up to 3 weeks, refrigerated)