Pat the brisket dry. Rub it with the salt, pepper, and paprika. Heat the oil in a large skillet over medium-high heat until it shimmers. Sear the brisket 3 to 4 minutes per side, until deeply browned. Searing is optional, but it adds roasted flavor that ketchup alone can't give you.

Layer the sliced onions and garlic on the bottom of a 6-quart slow cooker. This keeps the meat off the direct heat and flavors the sauce from below. Whisk together the ketchup, soup mix, broth, vinegar, brown sugar, and Worcestershire. Set the brisket fat side up on the onions and pour the sauce over it. Tuck in the bay leaves.

Cover and cook on low for 8 to 9 hours. Resist lifting the lid, since each peek adds 15 to 20 minutes to the cook time. It's done when a fork slides in with almost no resistance and the internal temperature reads 195 to 205°F (90 to 96°C). If it still feels tight, give it another 45 to 60 minutes.

Move the brisket to a cutting board and tent it with foil for 20 minutes. Discard the bay leaves and spoon the fat off the surface of the sauce. Slow cookers trap moisture, so the sauce will be thinner than you expect. Pour it into a saucepan and simmer 8 to 10 minutes until it coats a spoon. Or stir the cornstarch into the cold water and whisk it in, then simmer for 2 minutes.

Look at the direction of the muscle fibers and slice across them into 1/4-inch slices. Slicing with the grain gives you stringy meat even when the brisket is fully tender. Return the slices to the sauce for 5 minutes to soak it up. Serve over mashed potatoes, buttered egg noodles, or dumplings. Rebecca's Tip: Make it a day ahead. Chill the brisket in its sauce overnight, and the fat rises into a solid cap you can lift off in seconds, which gives you a leaner dish without losing flavor. Cold brisket also slices far more cleanly. Reheat the slices in the sauce, covered, at 300°F for about 25 minutes.