1.Wash chicken under cold water; pat dry with absorbent paper. Using fingertips, carefully ease skin away from chicken breasts and thighs.
2.Combine butter, chopped tarragon and garlic in small bowl.
3.Place chicken on oiled wire rack in large baking dish. Push butter mixture and tarragon sprigs under chicken skin. Tie legs together with kitchen string. Cover; refrigerate 2 hours.
4.Preheat oven to 200°C/400°F.
5.Rub chicken with oil; season. Place potatoes around chicken; roast, uncovered, 20 minutes.
6.Reduce oven to 180°C/350°F; roast about 40 minutes or until chicken is cooked. Remove chicken from dish; cover, stand 10 minutes. Roast potatoes further 10 minutes or until browned and crisp.
7.Serve chicken with potatoes.