Heat cast iron pan over high heat with a little oil. When hot, add veal roast and sear all sides. (approximately 2 minutes per side) Place veal roast in double layer of tinfoil and securely wrap. Cook on tray in preheated oven for approximately 1 hour.
In the interim, cook Mornay sauce. To cook, melt the butter in saucepan, stir in flour and mix with a whisk. Add the cold milk and continue whisking until the sauce has thickened and you have no lumps. Add salt, pepper, and cheese, continue to stir until incorporated and cheese has melted. Grate nutmeg and incorporate into sauce. Add salt, pepper and more nutmeg to taste.
In a large skillet, saute the mushrooms and shallots until they are cooked (about 10-15 minutes) then add ⅓ of the Mornay sauce.
When veal is done, remove from oven and cool for 15 minutes. Slice veal roast into 9 equal parts and place a layer of the mushroom sauce, slice of cheese, slice of bacon, and spoonful of Mornay Sauce between each layer. (I found using a meatloaf pan helpful in assembly.) Top the re-assembled roast with any left over mushrooms, cheese and Mornay Sauce and broil for about 15 minutes to melt cheese.
Recipe by Tout va bien! (tm) at https://christymajors.com/the-french-winophiles-the-st-emilion-affair/