1. Cut the hens along both sides of the backbone and remove the bone.
2. Lay the hen flat and insert two soaked wooden skewers through both sides.
3. Mix together the butter, salt, pepper, tarragon and rosemary in a mixing bowl.
4. Loosen the skin on each hen around the breasts and thighs.
5. Insert 1 tbsp of the herb butter mixture under the skin of each hen.
6. Brush the hen with butter setting the butter aside for basting.
7. Heat the grill temperature to medium high.
8. Lay the hens on the grill and cover the grill.
9. Grill for 25 minutes, basting as necessary, until the hens are brown and crispy.