Prep the beef and veggies. Pat the beef dry and season with salt and pepper. Chop all vegetables into even, bite-sized pieces so they cook at the same rate.
Optional sear for deeper flavor. Heat olive oil in a skillet over medium-high.
Sear the beef in batches until browned on two sides, about 2–3 minutes per side. Don’t overcrowd the pan. Transfer browned beef to the crockpot.
Build your flavor base. In the same skillet, add the onion and a pinch of salt.
Sauté 3–4 minutes until softened, then stir in garlic and tomato paste for 30 seconds. This caramelizes the paste and boosts depth. Add this mixture to the crockpot.
Add the vegetables and seasonings. Layer in carrots, celery, potatoes, and mushrooms.
Sprinkle with thyme, rosemary, paprika, and a little more salt and pepper. Add bay leaves.
Pour in liquids. Stir in Worcestershire and beef broth until everything is mostly submerged. If needed, add a bit more broth or water to barely cover the ingredients.
Cook low and slow. Cover and cook on Low for 8–9 hours or on High for 4–5 hours.
The beef should be very tender and the vegetables soft but not falling apart.
Thicken the stew. Stir together cornstarch and water, then pour it into the crockpot. Turn heat to High if it’s not already and cook 10–15 minutes until the broth thickens into a stew. For a thicker texture, mash a few potato pieces with the back of a spoon and stir.
Finish with peas and adjust seasoning. Stir in frozen peas for the last 10 minutes.
Taste and add more salt and pepper as needed. Remove bay leaves.
Serve and garnish. Ladle into bowls and top with chopped parsley. Serve with crusty bread or over buttery mashed potatoes for extra comfort.