1. For the pickled grapes, trim the stem end from each grape and pack into a heatproof jar. Bring the remaining ingredients to a simmer then pour over the grapes. Allow to cool at room temperature for 20 minutes, then refrigerate for at least one hour before using. The grapes will keep for about a week.

2. Heat the oven to 220C. Cut along either side of the backbone of the chicken with a heavy knife or kitchen scissors to remove it, then press firmly on the front of the chicken breast to flatten it. Chop the backbone into smaller pieces and place in a roasting tray with the onion.

3. Season the chicken well with salt on both sides and rub with the oil and the rosemary, leaving the rosemary in the tray. Place the chicken in the tray, pour in about a cup of stock or water. Roast the chicken for 45 minutes until the skin is browned and the chicken is cooked through. You may wish to switch the oven to its grill setting for the last 10 minutes for skin that is very browned.

4. Remove the cooked chicken from the pan and rest it for 10 minutes. Meanwhile, place the pan on a hob and simmer, adding the extra stock or water to deglaze the pan and scrape away any dark bits. Season the pan juices with a tablespoon or two of the grape-pickling liquid, then strain out the solids.

5. For the polenta, mix the water and milk together and bring to a simmer. Add the polenta and return to the simmer, stirring regularly for about 15 to 20 minutes until the polenta is the consistency of cake batter. Add the cheese and butter and mix well.

6. Scatter the chicken with the grapes and parsley and serve with the pan juices and the polenta.

TIPS:

- Roasting a chicken flat is not only a great time-saver: it also gives you more crisp chicken skin than ordinary roasting.

- If you have any grapes left over, try them with cheese and crackers.