Black garlic butter chicken with black garlic mayo

Preheat the oven to 200ºC, gas mark 6. In a bowl, use a fork to mash together the butter and 1 tbsp black garlic paste; season. In a large roasting tin, toss the sweet potato chunks with 2 tbsp olive oil; season. Put the chicken on a board, carefully lift the skin covering the breast and rub the black garlic butter over the flesh. Put half the sage and the (unsliced) lemon half into the cavity, giving the lemon a squeeze as it goes in. Season the bird all over, then sit it breast-side up on top of the sweet potatoes. Drizzle over the remaining oil.

Roast for 30 minutes, then toss the red onion wedges and lemon slices through the sweet potatoes. Baste the chicken with the juices and return to the oven for 15 minutes, then toss the remaining sage leaves through the vegetables. Roast for a further 15-40 minutes, until the chicken is cooked through with no pink meat remaining and the juices run clear.

When the chicken is cooked, transfer to a board to rest. In a small bowl, stir 1 tbsp of the cooking juices into the mayonnaise, then swirl through the remaining 1 tbsp black garlic paste. When ready to serve, remove the lemon and sage from the chicken cavity and discard. Carve the chicken to serve with the roasted vegetables and black garlic mayonnaise, plus some steamed Savoy cabbage, if liked.