Prepare the Chicken.Pat the chicken breasts dry and season both sides with salt and pepper.
Sear the Chicken.Heat olive oil in a large skillet over medium-high heat. Add the chicken breasts and cook 4–5 minutes per side, or until golden brown and nearly cooked through. Remove and set aside on a plate.
Sauté the Mushrooms.In the same pan, reduce the heat to medium and add the butter. Once melted, add the sliced mushrooms. Cook for 5–6 minutes, stirring occasionally, until the mushrooms are browned and have released their juices.
Add Garlic and Herbs.Stir in the minced garlic and thyme. Cook for 1 -2 minutes until fragrant.
Deglaze the Pan.Pour in the white wine, scraping up any browned bits from the bottom of the pan. Let it simmer for 2–3 minutes to reduce slightly.
Make the Cream Sauce.Stir in the heavy cream, chicken stock, Parmesan cheese, and Dijon mustard . Simmer gently until the sauce thickens, about 3–4 minutes.
Return Chicken to the Pan.Place the chicken breasts back into the sauce and spoon the creamy mushroom mixture over them. Simmer for 5 minutes, or until the chicken is fully cooked and the sauce has thickened to your liking.
Finish and Serve.Sprinkle with fresh parsley before serving