Coat the bottom of a large shallow cast iron skillet or braising pan with olive oil and heat on medium heat until hot. Season the chicken on both sides with salt and pepper and then brown, skin side down for about 15 minutes, until the skin is nice and crisp. Flip the chicken and cook for another 15 minutes, or until done. The meat should read 160F on an instant read thermometer. Set aside on a plate and cover with foil, or put in a warm oven while you make the sauce.
Add the shallot and garlic to the pan and saute, stirring constantly, for a couple of minutes. Then add the Marsala wine and let it bubble down while you scrape up the browned bits from the bottom of the pan.
Add the chicken stock, heavy cream, and sun dried tomatoes, and cook the sauce for a few minutes until it starts to thicken, stirring frequently. Scrape up everything from the bottom and sides of the pan into the sauce. NOTE: This isn't a super thick sauce, but it will thicken somewhat as it cooks.
Add the cheese and stir until incorporated. Add the chopped spinach and fresh tomatoes to the pan, and cook until the spinach has wilted. Add the chicken back into the pan and heat through before serving, garnished with fresh parsley or thyme.
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Notes
My husband's a dedicated thigh man, hence I used thighs, but this recipe is just as good with any chicken parts, and you can make a super quick meal with chicken cutlets, which are thinly sliced boneless skinless chicken breasts.
Use chopped chicken instead of the whole thighs, and serve this over pasta. The pasta absorbs all that creamy sauce and it's fantastic.
Cut calories and fat by using a little more chicken stock and less cream. Let the chicken stock reduce, and you can thicken the sauce with a little Wondra flour.
I use the sun-dried tomatoes that come in oil, in a jar, but if you only have the dry kind, re-hydrate them in warm water before using.
For no-alcohol version replace wine with chicken stock, although be aware that some of the alcohol evaporates off, and the flavor payoff is huge. Even a tablespoon or two will make a difference in the flavor of this sauce.