Place the chicken into a large freezer bag. Add buttermilk, 50ml olive oil, garlic, peppercorns, salt, thyme and honey. Seal bag securely and refrigerate 24 – 48 hours.
Heat oven to 170°C. Remove chicken from marinade and place on a rack to allow excess marinade drip off. Line a roasting pan with foil and place the chicken onto the pan. Drizzle with remaining 2 tablespoons of olive oil. Roast for 60 minutes and then increase heat to 200°C. Continue roasting until well browned and until juices run clear when pierced between the breast and the thigh.
Remove from the oven and allow to rest for 10 minutes before cutting into serving pieces. Drizzle each serving with pan juices.