Season the beef cubes evenly with salt, black pepper, and onion powder.
Place the seasoned beef cubes into the slow cooker basin.
In a small bowl, whisk together the beef broth, soy sauce, Worcestershire sauce, and minced garlic.
Pour the liquid mixture over the beef bites.
Place 4 tablespoons (half) of the cubed butter on top of the beef.
Cover and cook on low heat for 6 to 7 hours, or on high heat for 3 to 4 hours, until the beef is fork-tender.
Before serving, stir in the remaining 4 tablespoons of butter and the fresh parsley until the butter is completely melted and the sauce is emulsified.