If you using already cooked steak, cut into 1 inch cubes and set aside. In a heavy bottom pot over medium heat, add the butter and olive oil. Continue to 3rd step.
For fresh steak: In a heavy bottom pot over medium high heat, add the butter and olive oil. Cut the fresh steak into 1 inch cubes and season with salt. Sear all sides and then remove from the pot. work in batches so you do not overcrowd the pot. Set cooked steak aside.
In the same pot over medium heat, add the diced onion. Cook until the onion is browned and softened. Now add in the garlic, herbs, and mushrooms. Continue to cook until the mushrooms are browned and soft.
Add in the beef broth and the xanthan gum. Bring the soup to a boil and cook for a few minutes to let it thicken.
Add in the steak and cook for a few minutes to heat through. Ladle into bowls and serve.