Prep the chicken: Pat chicken dry. Season both sides with salt and pepper. If using flour, lightly dredge each piece and shake off the excess. This helps browning and thickens the sauce later.

Brown the chicken: Heat olive oil in a large skillet over medium-high. Add chicken and sear until deep golden, about 4–5 minutes per side. Transfer to a plate; it’ll finish cooking in the sauce.

Sauté the mushrooms: Reduce heat to medium. Add butter to the same skillet. Stir in mushrooms with a pinch of salt. Cook, without moving too much at first, until they release their liquid and turn golden at the edges, 6–8 minutes.

Aromatics in: Add shallot and cook 2 minutes. Stir in garlic and thyme for 30 seconds, just until fragrant. Scrape up browned bits—they’re flavor.

Deglaze: Pour in wine (if using) and simmer 1–2 minutes to reduce by half. Add chicken broth and bring to a lively simmer.

Creamy finish: Stir in cream and Dijon. Simmer 2–3 minutes until slightly thickened. If not using flour earlier, simmer a bit longer or add a cornstarch slurry (1 teaspoon cornstarch mixed with 1 tablespoon cold water) to help thicken.

Return chicken to pan: Nestle chicken into the sauce and reduce heat to medium-low. Simmer gently 5–8 minutes, flipping once, until chicken is cooked through (internal temp 165°F). Avoid a rolling boil to keep the sauce smooth.

Final touches: Stir in Parmesan until melted. Squeeze in a little lemon juice to brighten. Taste and adjust salt and pepper. Sprinkle with parsley.

Serve: Spoon over mashed potatoes, buttered noodles, rice, or cauliflower mash. Add extra sauce over the top.