Place the chicken, skin side up, in a single layer in a large, shallow, greased baking pan. To make the sauce, melt the butter in a medium-size saucepan over low heat. Add the onion and garlic and saute for about 5 minutes, or until the onion is translucent. Add the remaining ingredients and stir. Heat to boiling and pour over the chicken. Bake, uncovered, at 350 degrees F, basting occasionally, for 1 hour, or until a fork can be inserted into a chicken piece with ease. Serve hot.