Roast the chicken for about 20 minutes, or until the garlic is soft and golden. Transfer the garlic to a coarse sieve set over a small saucepan. Roast the chicken for about 1 hour longer, or until the juices in the cavity run clear. Tip the chicken in the pan to drain the juices, then transfer the bird to a carving board and cover loosely with foil. Skim the fat from the pan juices and reserve 1 tablespoon. Press the garlic through the sieve into the saucepan and pour in the pan juices with the peppercorns.