Heat a large casserole dish on medium-high heat (we used our Le Creuset). Add the pancetta and fry until the fat renders.

Remove the pancetta and fry the chicken in batches in the rendered fat. Add olive oil if needed, especially if using leaner bacon instead of pancetta. Remove the browned chicken pieces and set aside.

Return the pancetta to the pan and add the onions, celery, and mushrooms (if using). Sauté until the onions are translucent, being careful not to burn them. Add the garlic and sauté briefly until fragrant (do not brown).

Add the wine and cook for a minute or two to allow the alcohol to evaporate.

Return the chicken pieces to the pan. Add the canned tomatoes, rosemary, and bay leaf. If the mixture looks too dry, add a little water (we used just enough to rinse out the tomato tins). Cover and simmer for about 30 minutes, until the chicken is fully cooked.

If the sauce is too thin, remove the chicken and boil the sauce until it thickens to your liking. Then return the chicken to the pan and heat through.