Instructions:
- Season the chicken pieces generously. Heat butter and oil in a large Dutch oven over medium-high heat. Sear chicken in batches until nicely browned on all sides; remove and set aside, leaving fat in the pot.
- Reduce heat to medium. Add onions and mushrooms to the pot. Sauté until softened and mushrooms have released and reabsorbed their liquid (about 8–10 minutes). Add garlic and cook for 1 minute until fragrant.
- Sprinkle the flour over the vegetables. Stir constantly for 1 minute to cook out the raw flour taste.
- If using Calvados, pour it in and scrape up any brown bits (fond) from the bottom of the pot. Let it bubble for 30 seconds. Pour in the dry cider/wine and simmer until reduced by half.
- Gradually whisk in the warm chicken stock until smooth. Add the thyme sprigs and Dijon mustard. Bring to a gentle simmer.
- Return the seared chicken to the pot. Ensure the liquid mostly covers the chicken. Cover the pot tightly and transfer to a preheated oven at 350°F (175°C). Bake for 45 minutes.
- Carefully remove the pot from the oven. Stir in the heavy cream. Taste and adjust salt and pepper. Return to the oven, uncovered, for a final 10–15 minutes, or until the sauce has thickened nicely.
- Remove the thyme sprigs. Garnish generously with fresh parsley before serving straight from the casserole dish.