Mix salt, pepper, cumin and cayenne and rub mixtures over the chicken thighs.
In large heavy skillet, heat oil over medium high heat. Saute chicken until golden brown. Remove from pan. Drain, leaving 2 tablespoons fat.
Reduce heat to medium. Add onion and garlic and saute about 10 minutes.
Turn heat to high and add sherry to the onion and garlic mixture. Cook until the liquid is reduced, about 5 minutes. Add crushed tomatoes, bay leaves, olives,basil and salt and pepper to taste. Return chicken to pan.
Cook,covered, about 35 to 40 minutes,until chicken begins to fall away from the bone. Serve over couscous.