Pat beef dry, toss with flour, 1 tsp salt, and 1/2 tsp pepper. Sear in batches in hot oil over high heat, 2 to 3 minutes per side until deeply browned. Set aside.
Deglaze the skillet with a splash of broth, scraping up all browned bits. Pour into the slow cooker.
Layer potatoes, carrots, celery, and onion in the slow cooker. Add seared beef on top.
Whisk together remaining broth, tomato paste, Worcestershire, garlic, thyme, paprika, remaining salt and pepper. Pour over contents. Tuck in bay leaves.
Cook on low 8 to 9 hours or high 4 to 5 hours until beef is fall-apart tender and vegetables are completely soft.
Stir in cornstarch slurry in the last 30 minutes. Cook on high 20 to 30 minutes until broth is thick and glossy. Remove bay leaves. Serve with fresh parsley.