Arrange rack in upper third of oven; preheat oven to 450°.

Heat olive oil in a large skillet over medium-high heat. Pork sausage will need very little oil. Poultry sausage will need more. Add sausage and break up with a wooden turner or potato masher until the meat is super small. Sauté until a little browned, just cooked, but don’t stress if it’s not cooked all the way. Remove with a slotted spoon and transfer to a bowl.

If you haven’t seasoned the chicken with salt and pepper yet, do so now. Sear skin-side down in the same skillet and cook until golden brown on both sides, 8–10 minutes. You are not trying to cook them through. Transfer the chicken to a plate.

To the same skillet add onions, bell pepper, and garlic and saute over medium-high heat, scraping the bottom of the pan, until tender and beginning to brown, 6-8 minutes. Season with salt and pepper. The amount of salt you add will depend on the stock and how well you season the chicken. Add white wine and simmer, scraping the bottom of the pan (this is called deglazing), until reduced by half. Add tomatoes, chicken stock, vinegar, and rosemary and bring to a boil; cook until slightly reduced, about 5 minutes. Add reserved sausage back to the skillet and place chicken on top of the onion mixture, then transfer the skillet to the upper rack of the oven and roast the chicken for 10 minutes. Or until chicken is cooked through and an instant-read thermometer inserted into the thickest part of the thigh registers 165°. It’s hard to give an exact time for when the chicken is done since it will depend on the size of the thighs and how long you seared them in Step 3. The thermometer will tell you when they are done!

Remove rosemary sprigs. Garnish with parsley if desired.