Marinate the pork tenderloin in a resealable bag with the 3 cloves garlic, 1/4 cup olive oil, and herbes de provence at least one hour or overnight. Discard marinade before cooking.
Cut the tenderloins into 2 inch thick medallions and flatten each medallion slightly with the palm of your hand. They should flatten easily. Season both sides with salt and pepper.
Heat a large sauté pan over high heat. Add the olive oil and just 1 tablespoon of butter. Once heated, add the pork and allow to brown 2-3 minutes on each side. Once both sides have nicely browned, remove from pan, transfer to clean plate, and loosely tent with aluminum foil.
Using the same pan, melt the remaining 2 tablespoons of butter and add the shallots. Cook for about a minute until they start to brown and then add the garlic to cook for just a minute more. Stir while scraping the bottom of the pan to release any browned bits.
Add the mushrooms, stir well to distribute butter and flavor, and allow them to cook undisturbed for a couple of minutes before stirring. This will allow your mushrooms to get slightly brown. Continue to cook until the liquid has evaporated and the mushrooms are golden, about 3 minutes. Sprinkle with the flour, stir, and allow the flour to cook for a couple of minutes until fragrant.
Add the Marsala wine and allow to cook down until almost completely evaporated. Then, add the chicken broth and cook for an additional 3-5 minutes while stirring occasionally. Reduce the heat to low and stir in the heavy cream and parsley. Then return the pork and any accumulated juices to the pan. Cook the pork in the mushroom sauce, flipping the meat once, until it's firm to the touch, about 2 to 4 minutes or until it's no longer pink inside. Add salt and pepper, as desired.
Serve over pasta or mashed potatoes and a crisp green salad.