Start by seasoning the chicken cutlets with salt and pepper on both sides. Heat 1 tablespoon of butter in a large skillet over medium heat. Once melted, add the chicken cutlets and cook for about 4-5 minutes on each side, or until golden brown and cooked through. Remove the chicken from the skillet and set aside.
In the same skillet, add the remaining tablespoon of butter. Once melted, add the chopped onion and sliced mushrooms. Sauté for about 5-7 minutes, until the onions are translucent and the mushrooms are browned. Stir in the minced garlic and cook for an additional minute until fragrant.
Sprinkle the flour over the mushroom mixture and stir well to combine. Gradually pour in the chicken stock, stirring constantly to avoid lumps. Add the thyme and basil, and let the sauce simmer for about 5 minutes until it thickens slightly.
Reduce the heat to low, then stir in the heavy cream and grated parmesan cheese. Allow the sauce to simmer for another 3-4 minutes until it is creamy and well combined. Taste and adjust seasoning with more salt and pepper if necessary.
Return the cooked chicken to the skillet, spooning the mushroom sauce over the top. Allow it to warm through for a couple of minutes. Serve the Chicken with Mushroom Sauce over a generous helping of your Perfect Mashed Potatoes, garnished with chopped parsley for a beautiful finish.