In large heavy bottomed pot, melt butter over medium heat. Sprinkle chicken cutlets with salt and pepper and place 3 into hot butter. Brown on each side and remove from pot. Brown remaining 3 cutlets on both sides and set aside.
Saute onions and mushrooms in remaining butter until tender, about 5 minutes. Stir in minced garlic plus some salt and pepper and cook another minute.
Sprinkle in flour and stir, scraping up brown bits from the bottom of the pan. Increase heat to medium high and pour in chicken stock, thyme and basil. Bring to boil to thicken sauce, then reduce to medium low heat.
Cook another 10 minutes. Right before serving, stir in cream, cheese and parsley. Serve over mashed potatoes.