Heat up your oven to 375 F.
Season the chicken with salt and pepper.
Heat up the butter or oil in a cast-iron skillet on medium heat.
When the oil is hot brown the chicken for 6 minutes on each side.
Transfer the chicken to a plate and set it aside.
Add onion and garlic and cook it for 5 minutes.
Add mushrooms, and sweat them for 5 minutes.
Deglaze the pan with wine until about 2 tablespoons of liquid are left.
Add chopped tarragon.
Add tomatoes and chicken stock and bring it to a boil.
Add the chicken to the pan, transfer the pan to the oven, and cook it for 45 minutes at 375 F.
If your sauce is not thick enough, combine 2 tablespoons of either gluten-free flour, arrowroot, or regular flour (if you eat gluten) with a 1/4 cup of water and mix well. You can add it to the sauce and cook it for 4 another minutes.
Remove the chicken from the oven, add butter (optional) and top it with chopped parsley. Serve with a side dish of your choice! Enjoy!