1. Preheat your oven to 375°F (190°C). Lightly grease a baking dish with olive oil.
2. Season the chicken breasts with salt and pepper. In a large skillet over medium heat, add olive oil and sear the chicken breasts until golden brown on both sides, about 5 minutes per side. Remove from the skillet and set aside.
3. In the same skillet, melt the butter and add the minced garlic. Sauté until fragrant, about 1 minute.
4. Stir in the heavy cream and chicken broth, bringing the mixture to a gentle simmer.
5. Add the mozzarella and Parmesan cheese, stirring until the cheese is completely melted and the sauce is smooth. Mix in the Italian seasoning and red pepper flakes if using. Adjust seasoning with salt and pepper to taste.
6. Place the chicken breasts in the prepared baking dish. Pour the creamy sauce over the chicken, then scatter fresh spinach leaves on top.
7. Bake in the preheated oven for 20-25 minutes, or until the chicken is cooked through and the spinach has wilted.
8. Remove from the oven and let it rest for a few minutes before serving. This allows the flavors to meld together beautifully.

One tip I’ve learned from cooking this dish multiple times: don’t rush the resting time after baking. It gives the sauce a chance to thicken up a bit more, making it even more heavenly.