Sauté the Flavorful Mushrooms: In a large skillet, melt the butter over medium-high heat. Add your sliced mushrooms and a pinch of salt and pepper. Sauté them until they're beautifully softened and nicely browned, about 3 to 4 minutes. Scoop these delicious mushrooms into your slow cooker.
Sear the Beef for Richness: Season your bite-sized beef pieces with salt and pepper. In the same skillet, brown half of the beef quickly on all sides to lock in the flavor. Transfer this browned beef, along with any pan juices, to the slow cooker. Repeat with the remaining beef.
Combine & Cook: Pour in the beef broth, minced garlic, tomato paste, Worcestershire sauce, and onion powder into the slow cooker. Give everything a good stir to mix well.
Let Your Slow Cooker Do the Work: Cover the slow cooker and let it work its magic on the low setting for about 8 hours, or on high for 5 hours, until the beef is wonderfully tender and falling apart.
Thicken the Delicious Gravy: Once cooked, carefully remove about one cup of the warm juices from the pot. In a small bowl, whisk in the glucomannan (or xanthan gum) until smooth. Pour this mixture back into the slow cooker and stir well to thicken the sauce into a rich gravy.
Serve & Enjoy: Taste and adjust the seasonings if needed. For a light and healthy meal, serve these tender beef tips over creamy mashed cauliflower or cauliflower rice, perhaps with a sprinkle of fresh herbs!