Step 1: Prep the chicken - Start by pounding the chicken to an even thickness. This is one of those little steps that makes a big difference. It helps the chicken cook evenly, which means no dry edges and no undercooked middle. Season both sides with salt and black pepper, then lightly dredge each piece in flour. Shake off the extra so you get a light coating, not a thick one.
Step 2: Sear the chicken - Heat the olive oil and 2 tablespoons butter in a large skillet over medium high heat. Once the pan is hot, add the chicken and cook for 4 to 5 minutes per side until it is golden brown. You are not trying to fuss with it too much here. Let it sit and get that beautiful crust. Once browned, transfer the chicken to a plate and set it aside.
Step 3: Cook the mushrooms - In that same skillet, add the sliced mushrooms. This is where the magic starts building. Let them cook for about 5 to 6 minutes until they are browned and most of their moisture has cooked off. Stir in the minced garlic and cook for another 30 seconds, just until fragrant.
Step 4: Deglaze the pan - Pour in the Marsala wine and use a wooden spoon to scrape up all those browned bits from the bottom of the skillet. That is pure flavor right there. Let the wine simmer for 2 to 3 minutes so it can reduce a bit and mellow out.
Step 5: Build the sauce - Add the chicken broth to the skillet and stir everything together. Return the chicken to the pan, along with any juices from the plate. Let it simmer for 5 to 8 minutes until the chicken is cooked through and the sauce has thickened slightly. The chicken should be tender, and the sauce should look rich and glossy.
Step 6: Finish the sauce - If you are using the heavy cream, stir it in now. Then add the final tablespoon of butter and stir until it melts into the sauce. This is the part that takes it from good to really lovely. The sauce turns silky and smooth and coats the chicken beautifully.
Step 7: Serve and enjoy - Sprinkle with fresh parsley if you like, then serve hot over pasta, mashed potatoes, or rice. Make sure you spoon plenty of sauce over everything. That is not optional in my book.