Melt 1/4 cup butter in large skillet over medium heat. Brown chicken in butter quickly and remove to 13 x9" baking pan. Add remaining 1/4 cup butter to skillet and brown the onions and mushrooms with the garlic and tarragon. Pour this sautéed mixture over chicken. Preheat oven to 350 degrees. Heat the cream, cheese and Amaretto in the skillet, whisking rapidly. Stir in capers and pour liquid over chicken. Bake in oven for 40 minutes or until chicken is cooked thoroughly.