1. Sauté Mushrooms: Get a large skillet hot over medium-high heat and melt the butter. Add your sliced mushrooms and sprinkle them with a pinch of salt and pepper. Sauté them until they're softened and nicely browned, which usually takes about 3 to 4 minutes. Transfer these flavorful mushrooms to your slow cooker.
2. Sear Beef: Season your bite-sized beef pieces generously with salt and pepper. In the same hot skillet, brown half of the beef quickly on all sides to develop a rich crust and seal in the flavors. Move this browned beef to the slow cooker. Repeat with the remaining beef, ensuring all the delicious pan juices also go into the slow cooker.
3. Combine Flavors: Pour in the beef broth, minced garlic, tomato paste, Worcestershire sauce, and onion powder into the slow cooker. Give everything a good stir to ensure all ingredients are well combined.
4. Slow Cook to Perfection: Cover your slow cooker and let it cook on the LOW setting for approximately 8 hours, or on HIGH for 5 hours. The goal is for the beef to become incredibly tender and practically fall apart.
5. Thicken the Gravy: Once the beef is cooked, carefully remove about one cup of the cooking liquid from the pot. In a separate bowl, whisk the glucomannan or xanthan gum into this liquid until it's smooth and lump-free. Pour this mixture back into the slow cooker and stir well to evenly thicken the savory gravy.
6. Serve & Enjoy: Taste the rich beef tips and adjust the seasonings (salt and pepper) if needed. Serve these comforting beef tips over creamy mashed cauliflower or cauliflower rice for a wholesome, low-carb meal. A sprinkle of fresh chopped herbs makes a lovely finishing touch!