Mix soy sauce, sugar, ketchup and garlic together and pour 3/4 over ribs in casserole dish. Bake, covered at 250°F for 2 to 2 1/2 hours, until the meat is just pulling away from the bones.
Transfer ribs to a BBQ, heated to medium. Baste with remaining 1/4 of mixture and finish off the ribs by charring the sugars in the sauce.
If desired, transfer the broth left in the casserole to a saucepan. Make a smooth paste from the flour and water and slowly whisk into the broth as you bring it to a slow boil until desired thickness is attained. Use as a “gravy” or dipping sauce.