Heat a large heavy casserole dish on medium high heat, then add a good drizzle of olive oil. Brown the chicken on both sides just until golden, then remove chicken from pot and set aside.
Lower heat to medium then add pancetta, cook until the fats start to render out, then add onion. Cook until onion is soft, about 5 minutes.
Add mushrooms and garlic and cook for further 1 minute.
Add the wine and simmer for 1-2 minutes, use a spatula to scrape any brown bits off the pan.
Return the chicken to the pot, arranging them in a single layer, then add the chopped tomato. Sprinkle over with sugar and add the rosemary and bay leaf on top.
Bring to a boil, then reduce heat to low. Cover pot with lid and leave to simmer for about 15 minutes.
Uncover, season with salt and pepper to taste, then increase heat to medium and leave to cook until sauce has thickened, 10-15 minutes.
Garnish with chopped parsley and serve with soft polenta or crusty bread.