Pat the chuck roast dry.
Rub with salt, pepper, garlic powder, onion powder, and 1 tbsp Worcestershire sauce.
Heat olive oil in a large skillet over medium-high heat.
Sear the roast 3–4 minutes per side until deeply browned.
Add onion, garlic, potatoes, and carrots to the bottom of the slow cooker.
In a bowl or measuring jug, whisk together beef broth, tomato paste, 1 tbsp Worcestershire sauce, thyme, and rosemary.
Pour over the vegetables.
Add bay leaves.
Place the seared roast on top of the vegetables.
Cover and cook: Low: 8–10 hours, High: 5–6 hours.
Transfer the roast and vegetables to a platter and keep warm.
Remove bay leaves.
Pour the cooking liquid into a saucepan, or use the slow cooker insert if stovetop-safe.
Mix cornstarch and cold water into a slurry.
Bring the liquid to a simmer and whisk in the slurry.
Cook 2–3 minutes until thickened into a glossy gravy.
Slice or shred the pot roast.
Spoon gravy over the meat and vegetables.
Finish with chopped parsley or thyme.
