Combine broth and cream in a pot over stove on high heat and bring to the boil. Add chosen herbs/spices, mix in and simmer for about 2 minutes. Remove from heat.
Sprinkle in xanthan gum bit by bit, whisking constantly until desired thickness is achieved. Be careful not to overdo it or the gravy could end up slimy.
Notes
Get chicken bone broth recipeGet beef bone broth recipeNutritional info - This will vary depending on whether you use chicken or beef bone broth and whether you add any flavourings. Without flavourings the carbs should still be close to 0g for the whole cup whether you use chicken or beef bone broth.