Prep the chicken: Pat the chicken dry with paper towels. Season both sides with salt, pepper, and garlic powder. This helps develop a good sear and keeps the meat juicy.

Sear the chicken: Heat the olive oil in a large skillet over medium-high. Add the chicken and cook until golden on both sides and nearly cooked through, about 4–5 minutes per side for thighs, a bit less for thin breasts. Transfer to a plate and tent with foil.

Sauté the mushrooms: Reduce heat to medium. Add butter to the same pan. Once melted, add sliced mushrooms with a pinch of salt. Cook, stirring occasionally, until they release moisture and turn golden, about 6–8 minutes.

Add aromatics: Stir in the minced garlic and thyme. Cook 30–60 seconds until fragrant. Don’t let the garlic brown too much or it will taste bitter.

Deglaze: Pour in the chicken broth and scrape up any browned bits from the bottom of the pan. Those bits add big flavor to the sauce.

Make it creamy: Stir in the heavy cream and Dijon. Bring to a gentle simmer. Let it reduce for 3–5 minutes, stirring, until slightly thickened. If using Parmesan, whisk it in now for more body.

Finish the chicken: Return the chicken and any juices to the pan. Simmer on low for 3–5 minutes, spooning sauce over the top, until the chicken is cooked through and the sauce coats the back of a spoon.

Adjust and serve: Taste and add salt and pepper if needed. A tiny squeeze of lemon brightens the richness. Sprinkle with parsley and serve hot.