Place saucepan on stovetop over medium heat.

Add first 5 ingredients and bring to a boil. Mash berries with potato masher or use immersion blender to break up berries.

Add glucomannan and whisk briskly to combine.

If you prefer a smoother sauce, pour into heat safe blender and blend briefly; return to saucepan and continue cooking for 5 minutes, whisking regularly.

Store in mason jar.