NOTE: If using any flavor variation, see notes below* for when to add in the ingredients.
Bring heavy cream (1 3/4 cups) to a simmer in a heavy-bottom saucepan. Continue to cook at a simmer for 30 minutes, and watch carefully to maintain a simmer, not a boil -- you'll know you've reached the right temp when small bubbles continue to form around the edges. Whisk occasionally to fully incorporate bubbles with the cream.
Remove cream from heat, and whisk in erythritol (1 1/4 cups), unsalted butter (2 tablespoons), vanilla extract (1 teaspoon), and lastly xanthan gum (1/2 teaspoon). You want to sprinkle the xanthan gum over the top a little at a time so it dissolves without clumping.
Transfer the cream to a large bowl and allow it to come to room temp by placing it in the fridge for an hour.
Once the reduced cream has cooled to room temp, use an electric mixer to whip the cream for 3 minutes - we want to get the cream light and fluffy while incorporating everything.
In a second large bowl, whip the remaining heavy cream (2 cups) with an electric mixer until you've formed soft peaks.
Use a rubber spatula to gently combine the reduced cream and heavy cream. Make sure ingredients are seamlessly incorporated, but be gentle here to help maintain their fluff.
Transfer the mixture to an insulated tub or container and freeze for 4-6 hours. Enjoy!