Slice the chicken breasts in half to make two thin slices. Cover with plastic and pound to a thin and even thickness. Pat dry.
Combine the flour and spices for the chicken in a shallow dish. Coat each piece of chicken in this mixture, shake off the excess, and place on a dry surface.
Add 2 tablespoons of butter and the oil to a large pan over medium heat. Once the skillet is hot, add the chicken and cook for 5 minutes or until golden brown. Add additional tablespoons of butter one at a time if the skillet becomes dry while cooking the chicken.
If needed, add another tablespoon of butter. Once melted, add the tomatoes, shallots, garlic, and red pepper flakes and cook for 2 minutes. Reduce to low heat and stir in the heavy cream. Mix the chicken broth and the cornstarch and then add the mixture to your skillet.
Add in all of the sauce seasonings and bring the sauce to a simmer while scraping the bottom for any brown bits. Simmer until the sauce has thickened, about 5 minutes.
Once thickened, reduce heat to medium-low and stir in the Parmesan cheese, and cook until melted, about 2 minutes. Add in the spinach and cook for 1-2 minutes.
Finally, serve over your favorite starch and enjoy!
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Notes
Store Chicken Florentine leftovers in an airtight container in the refrigerator for up to 3 days. You can freeze it for up to 2 months; however, be aware that the cream sauce may separate slightly when thawed.Reheat it in a pan over low heat, stirring gently until heated through. If frozen, thaw it in the refrigerator overnight before reheating. To prevent the sauce from becoming too thick upon reheating, you may need to add a little broth or water to adjust the consistency.