Step 1: Season and Sear the Chicken
Pat the chicken thighs completely dry with paper towels. This is crucial for crispy skin. Season both sides generously with salt and pepper. Heat the olive oil in a large, heavy-bottomed skillet (cast iron or stainless steel) over medium-high heat. Once hot, add the chicken thighs skin-side down. Sear without moving for 6-8 minutes, until the skin is deeply golden brown and crisp. Flip and sear for 2-3 minutes on the other side. Transfer the chicken to a plate. It will not be fully cooked.

Step 2: Sauté the Mushrooms
Reduce the heat to medium. Add 1 tablespoon of butter to the skillet. Add the sliced mushrooms in a single layer if possible. Let them cook undisturbed for 3-4 minutes to develop color, then stir and continue cooking for 5-7 minutes total until they have released their liquid, the liquid has evaporated, and the mushrooms are golden brown. Season with a pinch of salt. Transfer the mushrooms to a bowl.

Step 3: Build the Aromatic Base
Add the remaining 2 tablespoons of butter to the skillet. Add the diced shallots and cook for 3-4 minutes until soft and translucent. Add the minced garlic and thyme and cook for 1 more minute until fragrant.

Step 4: Make the Roux (Optional for Thickening)
If using flour for a thicker sauce, sprinkle it over the shallot mixture and cook, stirring constantly, for 1-2 minutes to form a light roux and cook out the raw flour taste.

Step 5: Deglaze and Create the Sauce Base
Pour in the white wine (or broth) to deglaze the pan, scraping up all the flavorful browned bits from the bottom. Let it simmer for 2-3 minutes until reduced by about half. Stir in the chicken broth, heavy cream, and any optional ingredients like Dijon or Worcestershire. Bring to a gentle simmer.

Step 6: Combine and Simmer
Return the sautéed mushrooms and any accumulated juices to the skillet. Nestle the seared chicken thighs, skin-side up, into the sauce, along with any juices from the plate. Reduce heat to medium-low, cover, and let simmer gently for 15-20 minutes, until the chicken is cooked through (internal temperature of 165°F / 74°C at the thickest part).

Step 7: Finish the Sauce
Once the chicken is cooked, remove the skillet from the heat. Stir in the grated Parmesan cheese and fresh parsley until the cheese is melted. For a richer, glossier finish, you can stir in an extra tablespoon of cold butter at the end. Taste the sauce and adjust seasoning with salt and pepper.

Step 8: Rest, Garnish, and Serve
Let the dish rest, covered, for 5 minutes. This allows the sauce to thicken slightly and the chicken to reabsorb its juices. Garnish with additional fresh parsley. Serve hot, spooning the creamy mushrooms and plenty of sauce over each chicken thigh