Remove roast from refrigerator and let stand while you prepare vegetables.
Using a sharp knife, pierce meat about ½-inch deep and insert slivers of garlic in each hole, pushing all the way in. Spray roast lightly with olive oil cooking spray and season generously with salt, pepper and dried rosemary.
Heat a large non-stick skillet over medium-high heat. Brown roast on all sides, about 4 minutes per side. Transfer to slow cooker.
Place potatoes, carrots and any remaining garlic around roast. Pour 1 cup beef broth over vegetables.
Cover and cook on low 6-8 hours or until roast and veggies are tender.
Remove roast from slow cooker and slice.
Whisk remaining 2 cups beef broth with 2 tablespoons cornstarch to make a slurry; stir into slow cooker. Turn to high; add roast back to slow cooker, cover and cook an additional 15 minutes until thickened.