Preheat the oven to 180ºC (360ºF). Wash the chicken under cold running water and dry with paper towel.
Combine the oil, sage, and rosemary in a small bowl and season with salt and pepper. Rub the the herb mixture over the chicken. Put the sliced garlic inside the cavity. Place the chicken in a roasting pan.
Place the washed potatoes in a large bowl. Add the oil, rosemary sprigs and garlic, and toss well to coat. Season with salt and pepper.
Arrange the sliced potatoes around the chicken, in a roasting pan. Cook in the oven for 50 minutes, basting occassionally with the pan juices, until both are tender and golden brown.
Slice the chicken into pieces. Transfer to a serving platter with roasted potatoes. Pour the pan juices over the chicken and serve.
