Season the brisket with salt and pepper. Brown it in the oil for 5 minutes per side and place it fat-side up in a large slow cooker.
Cook the onions in the skillet for 7 minutes. Add the garlic and tomato paste and cook for 1 minute.
Stir in the crushed tomatoes, broth, Worcestershire, brown sugar and paprika. Scrape the skillet and pour the sauce around the brisket; add the bay leaves.
Cover and cook on low for 8 to 9 hours, until a fork slides into the thickest part easily but the meat is not falling apart. Discard the bay leaves.
Rest brisket 20 minutes; slice thinly across the grain. Skim sauce; spoon over slices.