These ribs are so sticky good you may want to put finger bowls—warm water with lemon slices—on the table, along with plenty of napkins. And don't be intimidated by making your own spice rub or barbecue glaze; it's as easy as stirring.
Rinse ribs with cold water and pat dry with paper towels. Cut between bones and arrange in a 13x9-inch baking dish.
Then make the rub: In a small bowl, stir together brown sugar, paprika, salt, onion powder, and cayenne. Coat each rib with rub, cover with aluminum foil, and chill at least 2 hours (up to overnight).
Preheat oven to 350°. When hot, transfer ribs, covered with foil, to oven and bake 30 minutes.
Meanwhile, make the glaze: Put oil in a small saucepan over medium-high heat. Add garlic and onion; cook until translucent, 5 minutes. Add remaining ingredients. Whisk together; simmer over medium-high heat, stirring occasionally, 10 minutes.
Remove ribs from oven and turn to coat. Cover and return to oven; bake 30 minutes more. Remove and baste with a third of the glaze, turning with tongs to coat. Return to oven uncovered, reduce heat to 325°, and bake until tender, 30 to 45 minutes more. Remove and coat with another third of the glaze. Serve with remaining glaze on the side.