Place the cubed beef into the slow cooker and season with salt, pepper, onion powder, thyme, and rosemary.
In a small bowl, whisk together the beef broth, soy sauce, Worcestershire sauce, and minced garlic.
Pour the liquid mixture over the beef cubes in the slow cooker.
Distribute the cubed butter evenly over the top of the beef.
Cover and cook on low for 4 to 6 hours or on high for 2 to 3 hours until the beef is tender.
In a small bowl, whisk cornstarch and cold water to create a slurry.
Stir the slurry into the slow cooker 30 minutes before serving and cook on high until the sauce thickens.
Serve warm, optionally garnished with fresh parsley.