Brown Beef Cubes:
Sprinkle salt and pepper over beef cubes. In a large skillet over medium-high heat, warm vegetable oil. Brown beef in batches, turning to get all sides golden, roughly 3-4 minutes per batch. Move browned meat to slow cooker.Sauté Onion Garlic:
Using the same skillet, sauté diced onion until softened, about 5 minutes. Stir in minced garlic and cook for 1 minute until aromatic. Transfer onion mixture to slow cooker.Make Broth Mixture:
In a separate bowl, combine beef broth, tomato paste, Worcestershire sauce, dried thyme, and dried rosemary; whisk until smooth. Pour this liquid over the beef and onions in the slow cooker. Drop in bay leaves.Layer Vegetables on Top:
Arrange chopped carrots, potatoes, and celery on top of the meat and liquid; do not mix.Slow Cook Stew:
Secure lid and cook on low for 7-8 hours or on high for 4-5 hours, until beef and vegetables are fork-tender.Thicken with Slurry:
In a small bowl, blend flour with cold water until no lumps remain. Stir this slurry into the stew. Replace lid and cook on high for 30 minutes to thicken.Season and Serve:
Discard bay leaves. Fold in fresh parsley. Adjust seasoning with extra salt and pepper if desired. Serve immediately.