Prep the veal if necessary so you end up with 6 thin scallopini styled cutlets.
Before you start cooking the veal, prep the mushrooms and saute in 1 tablespoon of butter until just tender. Transfer to a plate and reserve.
Heat a frying pan large enough to cook all 6 cutlets over medium-high heat. If you don't have a pan big enough to accommodate all 6, cook the cutlets in batches of 3.
Add the oil & 1 tablespoon of butter to the pan.
While the butter melts and the oil heats up, dredge each cutlet in seasoned flour. Be sure to shake off all excess or the flour will burn and stick to the pan.
Pan fry the cutlets for approximately 1 minute per side. Transfer the veal to a plate and cover with foil to keep warm.
Discard remaining oil in the pan and reduce heat to medium.
Add shallot, thyme, salt and pepper and cook for 1 minute. Remember to keep stirring so nothing burns.
Add Marsala wine and reduce by half.
Add demi glace, stir and cook until the sauce is thick enough to coat the back of a spoon. At this time I like to add the remaining tablespoon of butter to the pan. It's called mounting and helps "finish" the sauce.
At this time, I may add the previously cooked mushrooms back to the pan to reheat in the sauce or I may just add them to the top of veal as a garnish. You decide.
Taste and correct seasonings with salt & pepper.
Transfer the cooked veal cutlets back to the pan to reheat before serving. I like to spoon the sauce over the cutlets at this time while they are heating up.
Serve with pasta or rice and a favorite vegetable side dish.