Place ribs, onions and bay leaf in slow cooker. Whisk together broth, half the teriyaki sauce, sugar, tomato paste, flour, garlic and pepper. Pour over ribs. Cover and cook on LOW for 8 hours, or until ribs are tender and sauce is thick and sticky.
Remove ribs to a platter. Remove and discard bay leaf and any excess fat that has risen to the top. Measure out 1 cup (250 mL) of cooking liquid and place in a small saucepan. Bring to a boil over medium-high heat and reduce to a sticky glaze, about 10 min. Stir in remaining teriyaki sauce and serve over ribs.