Pat the steak cubes completely dry with paper towels - this is crucial for browning. Season all over with salt and pepper. Heat olive oil in a large skillet over medium-high heat until shimmering. Working in batches to avoid crowding, sear the beef for 2-3 minutes per side until deeply browned. Transfer to the slow cooker.

In the same hot skillet, pour in the beef broth and scrape up all the browned bits with a wooden spoon. Add Worcestershire, soy sauce, and garlic. Simmer for 1 minute, then pour over the beef in the slow cooker. Dot with 2 tablespoons of butter.

Cover and cook on LOW for 6-7 hours or HIGH for 3-4 hours, until the beef is fork-tender but not falling apart. Resist the urge to lift the lid during cooking.

Transfer the steak bites to a serving platter with a slotted spoon. Pour the cooking liquid into a small saucepan and bring to a boil over medium-high heat. Reduce until slightly thickened, about 5-7 minutes. Whisk in the remaining 2 tablespoons of butter for a glossy finish.

Pour the sauce over the steak bites, sprinkle with fresh parsley, and serve hot over mashed potatoes, buttered noodles, or crusty bread to soak up every drop.