In a mixing bowl, whisk together the heavy cream, almond milk, pumpkin puree, erythritol, vanilla, pumpkin pie spice, salt (and xanthan gum, if using) until the sweetener fully dissolves.
Pour the mixture into a Ninja Creami pint container. Seal and freeze on a level shelf for at least 24 hours, until completely solid.
Remove the pint from the freezer, install it into the Ninja Creami outer bowl, and attach the lid with the blade.
Lock the bowl into the machine and run the "Ice Cream" function.
Check the texture. If crumbly or too firm, run the "Re-spin" function until smooth and creamy.
Scoop and serve immediately, or add mix-ins and run the "Mix-In" cycle. Store leftovers in the freezer.