Pat beef dry and season all over with 2-1/2 teaspoons of the salt and the pepper. Heat 1 tablespoon oil in a wide 5-to 6-quart heavy pot over medium-high heat until it shimmers. Brown beef on all sides, about 15 minutes, then transfer to a plate.
Cook onions with 1/2 teaspoon salt in remaining tablespoon oil in pot, scraping up brown bits from bottom and stirring occasionally, until onions are well browned, about 25 minutes.
Meanwhile, preheat oven to 350°F with rack in middle.
Add beer to pot and bring to a boil. Add beef and meat juices from plate and return to a boil. Add 1 package of sauerkraut.
Cover pot and braise in oven until meat is very tender when pierced in several places with a meat fork, about 3 1/2 hours.
Transfer beef to a cutting board and let stand, loosely covered, 20 minutes. Cut off string, then slice meat. Skim off fat from sauce and discard bay leaf.
Serve braised beef with more hot sauerkraut and sauce.
Even better the second day. Refrigerate over night. Skim off solidified fat and reheat.