Pat the roast dry; season all sides with salt and pepper.
Heat olive oil in a skillet over medium-high. Sear roast 3–4 minutes per side.
Layer potatoes, carrots, onion, celery, and garlic in the slow cooker.
Whisk broth, Worcestershire, tomato paste, rosemary, and thyme. Pour over the vegetables.
Set roast on top. Cover and cook on Low 8–9 hours or High 4–5 hours.
Transfer beef and vegetables to a platter. Tent with foil to keep warm.
Skim fat from cooking juices. Bring 2 cups to a simmer in a saucepan.
Stir cornstarch with cold water. Whisk into juices and simmer until thickened.
Slice or shred the roast. Serve with vegetables and plenty of gravy.