Put ribs in a large pot or Dutch oven and cover with cold water. Bring to a boil, then cover and reduce heat to simmer. Cook until fork-tender, about 1 hour, skimming water occasionally to remove foam. Transfer to a large baking pan. Preheat oven to 350°.
In a medium saucepan over medium heat, cook onion and garlic in oil until soft, about 3 minutes. Stir in remaining ingredients except demi-glace or concentrated chicken broth and bring to a boil. Cook until sauce reduces by half, 10 to 15 minutes. Stir in the demi-glace or concentrated chicken broth.
Pour half the sauce over the ribs and bake, turning once, until the ribs begin to brown, 30 to 40 minutes. Serve 4 or more ribs per person with remaining sauce. Serves 4 to 6.