Pat beef dry, season with salt and pepper.
Sear in hot oil 1–2 minutes per side in batches.
Whisk broth, soy sauce, Worcestershire, brown sugar, tomato paste, garlic, paprika, onion powder, and red pepper flakes.
Add beef (and veggies if using) to crockpot. Pour sauce over.
Cover; cook on low 6–8 hours or high 3–4 hours until tender.
(Optional) Stir in cornstarch slurry 20 mins before serving; cook until thick.
Stir in cornstarch slurry 20 mins before serving; cook until thick.
Serve over potatoes, rice, or noodles. Garnish if desired.