Heat avocado, olive, or coconut oil in large pot or skillet over medium high heat. Add the beef and brown. Drain off fat if desired and set aside.
Using the same skillet, add the butter, onion, and mushrooms. If the mushrooms are large use a wooden spoon to chop 'em up a bit. Cook until veggies are soft, about 3-5 minutes.
Add the garlic and stir until fragrant, about 30 seconds. Stir in the beef broth and bring mixture to a boil.
In a small bowl, mix the arrowroot and water or non-dairy milk. When mixture reaches a boil, add the arrowroot mixture and stir constantly until thickened, about 1 minute.
Remove from heat and stir in the coconut cream until melted. If it has trouble melting, place on top of the burner you were using (that's now off) and stir until it completely melts. Add the beef, apple cider vinegar, salt, pepper, garlic powder, and mustard. Taste and adjust seasonings to your liking.
For coconut cream, place a can of full-fat canned coconut milk in the fridge for 24 hours. Then, scoop out the coagulated cream. I recommend Thai Kitchen, Sprouts, or Native Forest brands. Other brands may lend an aftertaste or not separate as well.
If you're not dairy-free, feel free to replace the coconut cream and apple cider vinegar with ¾ cup sour cream.