Start off by slicing 8 ounces of brown mushrooms into thick slices and keeping them aside. Mince two large garlic cloves and finely chop 2 tablespoons of fresh parsley, reserving some to garnish later. Cut each chicken breast in half lengthwise so you have 4 equal cutlets.
Next, place the chicken between plastic wrap and gently pound or hammer until the cutlets are about 1/3″ thick. Now season each side of the chicken with a mixture of 1/2 teaspoon salt and 1/4 teaspoon pepper, then lightly dredge them in some flour.
Now it’s time to heat up a large, heavy-bottomed pan over medium heat and add butter and olive oil. Once the butter and olive oil are hot, add the chicken to the pan and cook until both sides turn golden brown and it’s cooked through (approximately 3-4 minutes per side). If needed, add more oil to the pan along with the mushrooms and sauté until all of the excess liquid has evaporated and they’ve turned golden brown.
Then add the onion powder and garlic cloves, stirring for an additional 30 seconds until fragrant. Pour in the Marsala wine, continuing to stir while cooking until most of the liquids have reduced (about 4-5 minutes).
Next, slowly stream in the chicken stock and heavy cream, reducing the heat to a simmer so it can thicken (an additional 4-5 minutes). Taste the sauce and season with more salt if needed.
Return the cooked chicken to the pan, then sprinkle on some freshly chopped parsley. Spoon the delicious creamy Marsala sauce overtop and cook until everything is heated through and the sauce has thickened to your liking!