Arrange beef in the crockpot of the slow cooker. Cover with mushrooms, onion, and garlic.
1 ½ pounds chuck roast, 2 cups mushrooms, 1 small onion, 1 clove garlic
Pour bone broth and apple cider vinegar over the ingredients. Season with salt and pepper.
1 cup bone broth, 1 tablespoon raw apple cider vinegar, ½ teaspoon salt, ¼ teaspoon ground black pepper
Cover with the lid and turn the slow cooker on. Cook on LOW for 6-8 hours or HIGH for 3-4 hours.
Add the sour cream and stir well to combine in the last 15-30 minutes of cooking time. If you desire a thicker sauce, sprinkle xanthan gum over the top of everything evenly and mix well.
1 cup sour cream, 1 teaspoon xanthan gum
Remove from heat and serve warm over cauliflower rice, miracle rice, or zoodles. See notes for details.