For basting sauce: Whisk all ingredients in medium bowl to blend.
For ribs: Mix first 7 ingredients in small bowl. Using small sharp knife, loosen membrane from underside of each rib rack and pull off (or score membrane). Rub 1 tablespoon seasoning mix into each side of each rib rack. Place ribs in large roasting pan. Cover and chill at least 6 hours and up to 1 day.
Preheat oven to 325°F. Lift ribs from pan. Scatter onion, cinnamon stick, and ginger in pan. Pour in cider. Return ribs, meat side down, to pan; cover pan with foil. Roast ribs until meat is tender and begins to pull away from bones, about 2 hours. Uncover; cool at least 30 minutes and up to 2 hours.
Prepare barbecue (medium-high heat). Grill ribs until heated through and slightly charred, about 5 minutes per side. Brush generously on all sides with basting sauce. Grill until sauce becomes sticky glaze, about 3 minutes longer per side. Transfer rib racks to cutting board. Cut racks between bones into individual ribs. Arrange on platter and serve, passing remaining sauce separately.