1. Preheat the oven to 350 F.
2. Over a medium-high flame, heat butter, and oil in the skillet or cast iron pan. Meanwhile, dust the chicken with flour. When the oil is hot but not smoking, add the chicken and brown it on both sides, 3-4 minutes per side.
3. Remove to the baking dish. Be sure to wash your hands thoroughly after handling raw chicken.
4. After they have cooled a bit, spread the top of each piece with mustard. Put it in the oven while you make the sauce.

The Sauce

1. Add onions to the same skillet and sweat them for a couple of minutes. Toss in the garlic for just another 30 seconds. Do not let them brown, or they will turn bitter.
2. Add the mushrooms (and another pat of butter if needed) and sauté, occasionally stirring, until the mushrooms begin to give up their moisture.
3. Reduce the heat to medium and stir in the parsley, cream, and seasonings. Taste and adjust the seasonings as necessary. You may not need much pepper because of the mustard. Allow the mixture to just heat through.
4. Pull the chicken out of the oven long enough to pour the sauce evenly overall. Return it to the oven and let it bake until the chicken is cooked through and the juices run clear when pierced with a fork. This will vary with the thickness of your chicken pieces.
5. Remove the dish and give the sauce one more taste. It should be heavenly, but you deserve the first taste. Add more salt only if you think it needs it.
6. Finish it with a few drops of lemon juice and serve over wide noodles or rice with your favorite green vegetable on the side. yields 4 servings