2-- lemon slices, about 1/4-inch thick with seeds removed
Rinse chicken and place in a gallon-size resealable bag. Add 1/2 cup limoncello, lemon juice, salt, red pepper flakes and shallots to bag. Seal bag and turn several times to mix ingredients; refrigerate overnight. Remove chicken from bag and discard marinade. Wrap prosciutto around chicken breasts and secure with toothpicks. Grill over medium heat for about 15 minutes, turning several times, until chicken is cooked through and prosciutto is crispy.
While chicken is cooking, stir together raisins, 2/3 cup limoncello and lemon slices in a small saucepan. Bring to a boil; reduce heat and simmer for 10 minutes or until most of the limoncello is absorbed by the raisins, pressing the lemon slices with the back of a spoon to release juices. Spoon over chicken and sprinkle with rosemary.