SLOW COOKER CHICKEN MARSALA

–4 boneless, skinless chicken breasts (2 pounds)

–½ cup flour

–½ teaspoon kosher salt, plus more to taste

–½ teaspoon black pepper, plus more to taste

–2 tablespoons butter, divided

–3 ounces pancetta, chopped

–½ pound mushrooms, sliced ⅛-inch thick

–3 cloves garlic, minced

–½ onion, minced

–1 cup Marsala cooking wine

–1 cup chicken stock

–½ cup water

–⅓ cup cornstarch

–Fresh parsley, chopped