Prep the beef. Pat the beef dry with paper towels and season well with salt and pepper.
Drying helps it brown instead of steam.
Sear for flavor. Heat olive oil in a large skillet over medium-high. Brown the beef in batches, 2–3 minutes per side. Don’t overcrowd the pan.
Transfer browned beef to the slow cooker.
Sauté aromatics. In the same skillet, add onion and a pinch of salt. Cook 3–4 minutes until softened. Stir in garlic for 30 seconds.
Add tomato paste, cook 1 minute to caramelize. Deglaze with red wine (if using), scraping up browned bits. Pour everything into the slow cooker.
Layer the vegetables. Add carrots, potatoes, and celery to the slow cooker.
Sprinkle in thyme, rosemary, and smoked paprika. Add bay leaves.
Add liquids. Pour in beef broth and Worcestershire sauce. Stir gently to combine.
The liquid should just about cover the ingredients.
Cook low and slow. Cover and cook on Low for 8–9 hours or High for 4–5 hours, until beef is very tender and vegetables are cooked through.
Thicken the stew. Stir the flour or cornstarch with water to form a smooth slurry. Remove bay leaves. Stir the slurry into the stew, cover, and cook on High for 15–20 minutes until slightly thickened.
Add peas and finish. Stir in peas during the last 10 minutes so they stay bright and tender.
Taste and adjust salt and pepper. Garnish with chopped parsley and serve hot.