Preheat over to 350°.

Cut chicken breasts into 4 pieces. Place the chicken on a cutting board and cover with plastic wrap. Using the flat side of a meat tenderizer, gently pound the chicken pieces to 1/4 inch thick. (the plastic wrap is to prevent chicken juice from splattering all over your kitchen.)

Heat 2 tablespoons olive oil in a skillet over medium heat.

Season the chicken pieces with salt and pepper. Put the flour on a plate or shallow dish (I usually use a Gladware container). Coat each side of the chicken with flour and shack off the excess.

Cooking in batches, cook the chicken in the skillet until golden brown, about 2-3 minutes per side.  Be sure to add a bit more oil between batches to prevent burning.

Place the chicken in a baking pan as they finish cooking.

After all the chicken is cooked, add 2 tablespoons olive oil to the skillet. Add the mushrooms and season with salt and pepper. Cook until the mushrooms are soft, about 3-5 minutes. Add the shallots and stir for about a minute.

Add the Marsala wine and cook for 2-3 minutes. Add the chicken stock. Reduce the liquid by half. 

Mix the 2 tablespoons of flour with the 2 tablespoons of water. Slowly pour the flour and water mixture around the edges of the skillet and stir completely. This will thicken the sauce. Add the butter and stir until it's melted.

Pour the mixture over the chicken in the baking pan.  Cover and bake for 15 minutes.

Garnish with the chopped fresh parsley.