Chunk meat into 1 inch cubes, season with salt, pepper, and garlic powder
Heat 1 tablespoon olive oil in a large skillet over medium high heat, and add beef to skillet, browning it on all sides, but do not cook throughout. I like to use thongs to pick up the meat to sear on all sides. Transfer beef to a 6-QT crock pot. Leave juices in the skillet for the next step.
Add 2 tablespoons butter, to the juices in skillet, and add in your onions, minced garlic and mushrooms. Quick sauté for 3-5 minutes until mushrooms start to release their juices. Transfer mushrooms, onions, garlic, and any juices to the crockpot and stir in with the beef
Add beef broth, and Worcestershire sauce to the crockpot and stir all the ingredients together
Place lid on slow cooker, and cook on high for 3-4 hours or on low for 5-7 hours, until beef is tender. Taste and season with additional salt and pepper as needed
30 minutes before it is done cooking, mix together in a small bowl the water and cornstarch. Stir it into the crockpot and allow it to thicken
Serve over mashed potatoes or pasta
Storage: Leftovers can be refrigerated in an airtight container for up to 4 days.