Heat the olive oil in a pot over medium high heat. Sauté the chicken, and season with basil, salt and pepper, about 3 minutes on each side. Remove the chicken and set aside.
Add the butter to the pot, then sauté the mushrooms. Allow them to get some good color, then push to one side. Add in the garlic and sauté for 20 seconds, careful not to burn it!
Deglaze the pot with the marsala wine, scraping up the brown bits on the bottom. Stir in the chicken stock and most of the parsley (reserving some for garnish) then add the chicken back in. Cook for 10 minutes over medium heat, uncovered.
Remove the chicken and cook another 5 minutes to allow the sauce to thicken. Stir in the mascarpone cheese and cook an additional 5 minutes or until thickened. Add the chicken back in just to heat it through. Top with a garnish of parsley and serve along side your favorite Keto-friendly veggie or salad!