Norton Reduction Plum Sauce: In a bowl pit, skin and mash the plums well. In a small saucepan place the red wine and the shallots.
Cook them on medium high for 4 to 6 minutes, or until the liquid is reduced to 3 tablespoons. Add the veal stock and plums and cook the sauce for 15 minutes, or until it is reduced by 1/4. While whisking constantly, add the pieces of butter one at a time. Stir salt in.
In the side of each filet mignon make a slit 2" long. Do not butterfly! Insert a paring knife through the slit and cut out a “pocket” inside the filet. Stuff the filets with alternating layers of the cheese and the mushrooms. Finish the top layer with the mushrooms. Press the slit together so that it closes. Secure with a toothpick if necessary
In a large skillet place the butter and heat it on medium high until melted. Add the stuffed filet mignons and sauté them for 4 to 6 minutes on each side, or until the desired doneness is achieved. Pour the Norton Wine Sauce over the top of the filets.