Season the chicken: Pat chicken dry. Sprinkle with salt, pepper, and paprika on both sides.
This helps with browning and flavor.
Sear for color: Heat olive oil in a large skillet over medium-high heat. Add chicken and sear until golden, about 4–5 minutes per side (thighs may take longer). Transfer to a plate; it will finish cooking in the sauce.
Cook the mushrooms: Reduce heat to medium.
Add butter to the same pan. When foamy, add mushrooms with a pinch of salt. Cook, undisturbed for 2 minutes, then stir occasionally until browned and their liquid evaporates, 5–7 minutes total.
Add garlic and thyme: Stir in garlic and thyme and cook 30–60 seconds, just until fragrant.
Don’t let the garlic burn.
Deglaze the pan: Pour in chicken broth and Dijon. Scrape up browned bits from the bottom of the pan—this is where the flavor lives. Let it simmer for 2 minutes.
Make it creamy: Lower the heat.
Stir in the cream and Parmesan (if using). Simmer gently until slightly thickened, 2–3 minutes. Taste and adjust salt and pepper.
Finish the chicken: Return chicken and any juices to the skillet.
Spoon sauce over the pieces and simmer until chicken is cooked through, 3–6 minutes depending on thickness. Internal temperature should reach 165°F/74°C.
Brighten and serve: Add a small squeeze of lemon if you like, and sprinkle with parsley. Serve hot over mashed potatoes, buttered noodles, rice, or with crusty bread.