1. Preheat oven to 350°. Spread onion slices evenly on a rimmed baking sheet, and place ribs, bone side down, on top. Pour beer over ribs, sprinkle with sea salt and pepper, and cover tightly with foil. Bake 3 hours or until tender.
2. Brush both sides of ribs with Chipotle Maple Barbecue Sauce. Grill over medium heat, meat side down, 10 to 15 minutes or until slightly charred and crispy, basting several times with sauce. Flip ribs over, and baste cooked side liberally. Close grill lid, and cook 10 to 15 minutes more, basting often. Remove from heat; let rest 10 minutes. Cut individual ribs apart, and serve warm.
Note: You can bake the ribs (step 1) up to a day ahead, but you'll need to leave them on the grill a few minutes longer to make sure they're heated through.