Step 1

In a large heavy saucepan, bring the whipping cream to a boil over medium heat. Reduce the heat and simmer gently for 30 minutes. Watch carefully as you want it to simmer but not continue to boil. There should be little bubbles along the edges the whole time.

Step 2

Remove from heat and whisk in the sweetener and butter until dissolved. Sprinkle the surface with 1/4 tsp xanthan gum and whisk vigorously to combine. Let cool 10 minutes. If it's not quite thick enough, whisk in the additional xanthan gum.