Pat dry, tendorize, and season chicken with salt and pepper.
Heat olive oil on med-high heat, in a large skillet.
Cook Chicken 5 minutes each side. (If you have to do this in bathces, it is OKAY.)
Take chicken off the skillet, and add to plate and set aside, with tented foil to keep it warm.
Add butter to same skillet, and let melt on med-high heat. Add shallots and cook, stirring often, until soft and fragrant about 1-2 minutes.
Add garlic, stirring frequently, until fragrant, about 30 seconds.
Now if you need to add just a little more olive oil to the pan, you can now, but don't overdue it. Add your mushrooms and saute until they shrink a little and are soft, about 4-5 miniutes.
Add flour and stir well to combine, until the flour isn't powdery anymore.
Add your marsala wine, followed by your chicken broth. Stir to combine, and scrape any brown bits on the bottom of the pan. Bring to a boil for a minute or two to let thicken and reduce.
Put chicken back in the pan with the marsala sauce, and ladle sauce on top. Serve Immediatley.
Enjoy!