Combine the berries, lemon juice, salt, and sweetener in a medium sauce pot on medium-low heat. Keep stirring while the berries heat up and release their juice. Use a potato masher or a sturdy whisk to smash up the berries.
After the berries have released a good amount of their juice, whisk in the xanthan gum. Continue cooking on low, whisking occasionally until the sauce reaches your desired thickness.
Remove from the heat and cool before adding to your storage container. Refrigerate or freeze for later.
Notes
I buy Gentle Sweet at www.trimhealthymama.com.I buy Swerve and Pyure at Wal-Mart.