Heat the olive oil in a large skillet over medium heat. Season the chicken with salt and pepper and brown on both sides in the skillet. (This step is absolutely optional. It adds a bit of good flavor and texture, but if you are in a hurry, skip it.)
1 tablespoon olive oil, 1 pound chicken, Salt and pepper
In the base of the slow cooker, combine the chicken stock, Marsala wine, and garlic.
1/2 cup chicken stock, 1/2 cup Marsala wine, 2 cloves garlic
Add the chicken to the slow cooker and top with the mushrooms. Cook on low for 2 to 3 hours or until the chicken reaches 165 degrees. (Read here about monitoring temperature of chicken in a slow cooker). 8 ounces sliced mushrooms
At the end of the cooking time, remove the chicken and tent with foil.
Whisk together 2 tablespoons warm water and 2 tablespoons corn starch. Stir it into the liquid in the crockpot so it is fully combined. Turn the crockpot to high and let cook (with the top off) for 5 minutes.
2 tablespoons corn starch
Stir in the heavy cream if using, and taste the sauce. Add more salt and pepper if necessary and then add the chicken back to the slow cooker, spooning the sauce over the top. Serve over fettuccine and enjoy.
2 tablespoons heavy cream, 8 ounces fettuccine