Combine first 7 ingredients in a large bowl. Add chicken, turning to coat.
Heat oil and butter in a tagine or Dutch oven over medium heat. Add chicken, skin side down, and cook 4 to 5 minutes per side or until golden brown. (Cook in batches, if necessary.) Transfer to a plate.
Using a separator, pour off the excess fat
Add garlic to pan, and sauté about 1 minute.
Add the onions and saute until soft, 5 minutes
Add mint, thyme, broth, chicken, and any juices that drained onto plate. Cover, reduce heat to low, and simmer 1 hour minutes or until chicken is tender.
Remove cover and simmer 1 hour to reduce sauce
Bring onion and next 3 ingredients to a simmer in a separate saucepan over low heat; cook 8 to 10 minutes or until lemon becomes soft and liquid thickens. Discard herb sprigs; pour glaze over chicken, and garnish, if desired.