Preheat oven to 400 degrees.

Season chicken generously with salt and pepper. Sprinkle all over with Herbs de Provence (or Italian seasoning).

In a large cast iron skillet (or other oven-safe skillet), combine oil and butter over medium-high heat.

Once butter is melted, add the chicken and brown on each side for 1-2 minutes until golden. Transfer to a plate and set aside.

In the same skillet, add the butter. Once melted, stir in garlic and mushrooms and saut? for 2-3 minutes until mushrooms are browned and garlic is fragrant.

Stir in chicken broth, heavy cream, dijon mustard, salt, and pepper. Bring to a boil and cook for two minutes at a high boil. Remove from heat.

Return chicken to skillet, spoon sauce over the chicken, then transfer skillet to the oven to bake for 15-20 minutes until chicken is cooked through and sauce has thickened.

Spoon the mushroom sauce over the chicken and serve.