1. Begin by seasoning the chicken breasts with salt, pepper, and Italian seasoning. In a skillet over medium-high heat, sear the chicken in olive oil until golden brown on both sides. Once seared, remove the chicken from the pan and set it aside.

2. In the same pan, melt the butter and add the chopped onion. Sauté the onion until it’s soft and translucent. Then, add the minced garlic and sliced mushrooms, continuing to sauté until the mushrooms are tender and lightly golden.

3. Sprinkle the flour over the mushroom mixture and stir to coat. Gradually pour in the chicken broth, whisking constantly to prevent any lumps from forming. Once the broth is incorporated, pour in the heavy cream and let the sauce simmer until it thickens slightly. Adjust the seasoning with additional salt and pepper to taste.

4. Preheat your oven to 375°F. Place the seared chicken breasts in a baking dish, then pour the creamy mushroom sauce over the top. Sprinkle the shredded mozzarella and grated parmesan cheese evenly over the dish.

5. Transfer the baking dish to the preheated oven and bake for 20-25 minutes, or until the chicken is cooked through and the cheese is melted, bubbly, and golden brown.