In a large skillet or Dutch oven, heat the olive oil over medium-high heat. Season the chicken thighs with salt and pepper, then add them to the skillet, skin-side down. Brown the chicken for about 5-7 minutes on each side until golden brown. Remove the chicken and set aside.
In the same skillet, add the Italian sausage pieces and cook until browned, about 5 minutes. Remove the sausage and set aside with the chicken.
Add the chopped onion to the skillet and sauté for 3-4 minutes until softened. Stir in the minced garlic and red pepper flakes, cooking for an additional minute until fragrant.
Pour in the chicken broth, white wine, and apple cider vinegar, scraping up any browned bits from the bottom of the skillet. Bring the mixture to a simmer.
Return the chicken and sausage to the skillet. Add the rosemary and thyme. Cover and simmer on low heat for about 30-35 minutes, or until the chicken is cooked through and tender.
Taste and adjust seasoning with salt and pepper as needed. If you prefer a thicker sauce, remove the lid and simmer for an additional 10 minutes to reduce.
Serve hot, garnished with fresh parsley.