Pat the chicken dry and season both sides with salt and pepper. This helps the chicken brown nicely in the pan.
Heat a large skillet over medium-high heat and add the olive oil. When the oil shimmers, add the chicken breasts. Cook for 4–5 minutes per side, or until deeply golden and cooked through. Remove from the pan and set aside to rest.
In the same skillet, add the butter. When it’s melted, toss in the sliced mushrooms. Sauté for 4–6 minutes until they release their moisture and start to brown. A little browning adds color and depth.
Add the minced garlic and sauté for about 30 seconds, just until fragrant. Avoid burning the garlic; it should smell nutty and inviting.
Pour in the chicken broth to deglaze the pan, scraping up any browned bits from the bottom. Those bits are flavor gold.
Stir in the heavy cream (or half-and-half) and bring the mixture to a gentle simmer. Let it thicken slightly, about 3–4 minutes.
Stir in the parmesan cheese until it melts into the sauce. If you’re using sun-dried tomato paste, add it now for a touch of sweetness and color.
Taste and adjust with salt, pepper, and lemon juice if you like a bright finish. Return the chicken to the pan and spoon some sauce over the top. Simmer for 1–2 minutes to reheat the chicken and meld the flavors.
Remove from heat. If you have fresh thyme, sprinkle it on top for a fresh aroma. Let the dish rest for a couple of minutes before serving to keep the chicken juicy.