1 - Coat slow cooker bowl with nonstick cooking spray.
2 - Place onion and garlic in slow cooker. Season beef with salt and pepper; place over onions. Arrange carrots, potatoes and celery around beef, in that order. Combine broth, tomato paste and thyme; pour over beef. Drizzle 1 tablespoon of the worchestershire sauce over top.
3 - Cover and cook on high for 6 hours or low for 8 hours.
4 - Remove beef from slow cooker and place on a serving platter. Spoon out vegetables with a slotted spoon and place around roast. Keep warm.
5 - Strain cooking liquid into a medium-size saucepan; skim off excess fat. Bring to a simmer. Combine cornstarch with 3 tablespoons water and stir into saucepan. Simmer for 1 minute until thickened. Stir in remaining tablespoon worchestershire sauce.
6 - Slice beef and serve with vegetables and gravy.
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