Pre-heat the oven to the lowest temperature possible – usually around 170˚F.

Slice the chicken breasts in half horizontally so you end up with four flat chicken cutlets. Lightly pound the cutlets to ½-inch thick. Season the chicken with salt and pepper, and then lightly dredge each breast in the flour, shaking off any excess.

Heat a large skillet over medium-high heat. Once the pan is hot, add 1 tablespoon of olive oil and one tablespoon of butter to the skillet. Place the chicken in the skillet, reduce the heat to medium and brown well on both sides – about 2 to 3 minutes per side. Brown the chicken in batches rather than over-crowding the skillet. Transfer the browned chicken to a platter and place it in the oven to keep warm.

Add the remaining olive oil to the skillet. Cook the mushrooms in the skillet over medium-high heat until nicely browned and tender – about 4 minutes, tossing occasionally. Add the garlic and the sage and continue to cook for another minute.

Add the Marsala wine to the skillet and bring to a simmer. Deglaze the skillet, scraping up any brown bits on the bottom of the skillet. Reduce the wine by half – about 3 to 4 minutes. Add the chicken stock and continue to simmer for another 3 to 4 minutes. If using cream, add the cream now and simmer for a minute or two. If using butter, remove the skillet from the heat and stir in the butter to melt. Stir in the parsley and season the sauce to taste with salt and pepper. Return the chicken and any juices to the skillet and turn to coat all the pieces with the sauce. Serve immediately.