In a large plastic freezer bag, mix together the flour, salt, pepper and Italian seasoning. Add chicken and shake to coat.
In a large skillet, melt butter in oil over medium heat. Add the garlic (you can add with the butter if frozen). Place chicken in the pan and lightly brown on both sides. Once chicken is brown, add mushrooms and shallot. Pour in wine, sherry and chicken stock. Cover and simmer chicken for about 10 minutes, turning once.
If you want a thicker sauce (like I do), add 2 teaspoons cornstarch to a little chicken stock and add to liquid in pan.
Once chicken and mushrooms are cooked, add the heavy cream.