Season ribs with salt and pepper. Heat oil in a large skillet over medium-high heat and brown the ribs in batches for 2 to 3 minutes per meaty side, then transfer to a 6-quart slow cooker.
Add shallots and garlic to the cooker. Pour lager into the hot skillet, scrape up the browned bits and pour over the ribs with stock and bay leaf.
Cover and cook on LOW for about 8 hours until the meat separates easily from the bones; continue in 30-minute increments if it still resists a fork.
Lift ribs onto a tray, remove every bone and any large fat seams and pull the meat into broad pieces. Strain the cooking liquid into a saucepan and skim the surface thoroughly.
Simmer the strained liquid for 10 to 15 minutes to concentrate it, then spoon about 1/2 cup over the beef to keep it moist. Keep beef hot while preparing the rolls.
Split rolls, add Havarti along the cut faces and broil for 1 to 2 minutes until the cheese melts and bread edges are lightly toasted. Divide the drained beef among the rolls.
Close and serve one sandwich per person with about 1/2 cup hot strained jus alongside. Reserve any extra jus separately rather than pouring it into the bread.