Preheat your oven to 375 degrees F.

Season your chicken breasts with Old Bay seasoning, making sure to evenly coat each piece.

In a large skillet, melt your butter over medium-high heat.

Add your chicken breasts to the skillet and cook for 4-5 minutes per side, or until golden brown.

Remove your chicken breasts from the skillet and transfer them to a baking dish.

In the same skillet, add your flour and whisk it into the butter until it's smooth and free of lumps.

Gradually pour in your milk and heavy cream, whisking constantly to prevent lumps.

Bring the mixture to a boil, then reduce the heat and let it simmer for 2-3 minutes, or until it thickens.

Remove the skillet from the heat and stir in your grated Parmesan cheese.

Pour the sauce over your chicken breasts and bake for 15-20 minutes, or until the chicken is cooked through and the sauce is bubbly.