Tuscan Chicken Cacciatore

3 lbs. boneless, skinless chicken breasts, cut into large pieces
6-8 large, ripe Roma or plum tomatoes--cored, peeled, seeded, and chopped (or one 28-oz can
Italian chopped tomatoes)
1 large sweet onion, thinly sliced
1 tsp. kosher or sea salt (or to taste)
1 tsp. freshly ground black pepper (or to taste)
1 Tbs. extra-virgin olive oil (or light olive oil, if you prefer)
4 cloves garlic, freshly minced
2 Tbs. fresh rosemary, chopped
1/2 cup white wine vinegar
1/2 cup dry white wine
3/4 cup reduced sodium, fat-free chicken stock
1 1/2 tsp. butter (light butters are acceptable)
1 1/2 tsp. all-purpose flour

Rinse the chicken chunks under cool water, dry with paper towels, and season with salt and pepper. In a large skillet or dutch oven, heat the oil over moderate heat. Add the garlic and saute until golden (about 1-2 minutes). Add the onions and cook until almost translucent.

Add the chicken and rosemary and cook, turning the chicken until it is brown on all sides. Increase the heat to high, add the vinegar and cook, scraping up the browned bits on the pan and incorporating that into the saute.

When vinegar is almost evaporated, reduce the heat to med-low and add the tomatoes and wine and cook until it is slightly reduced. Stir in the chicken stock, cover, and simmer.

Turn the chicken a couple of times until tender. Mash the butter and flour together until they form a thick paste. Add it to the pan and stir into the sauce until it is thickened and fully incorporated. Simmer a few more minutes. Serve hot over pasta.