Place each veal scallop between large sheets of plastic wrap on a work surface. Use the flat side of a meat mallet to pound lightly from the center outward, gently easing the veal to an even thickness, about 1/4 inch. The scallops should be roughly 8 by 4 inches. (This step may be done up to 4 hours in advance; refrigerate the scallops on a baking sheet, still sandwiched between sheets of plastic wrap, until 10 minutes before you are ready to cook them.)
Warm the wine in a small saucepan. Remove it from the heat, and add the sun~dried tomatoes. Let stand for 20 minutes to rehydrate. Drain, reserving the wine, and press or squeeze the tomatoes to remove excess liquid. Slice into julienne strips. Place a large saute pan over medium~high heat, and add olive oil.
Salt and pepper both sides of the veal. On a plate, spread a generous amount of flour for dredging. Dredge each scallop in the flour, and shake off the excess. Add the veal to the pan, and saute for 1 minute; then turn the veal and add the shallots. Cook for 1 minute, and add the sun~dried tomatoes, shiitakes, and button mushrooms. Reduce the heat slightly, and cook for 2 minutes more, stirring occasionally. Add the reserved white wine and the marsala, and simmer until the vegetables are tender, about 3 minutes. Add the Veal demiglace, 1/2 teaspoon fine sea salt, and 7 to 8 turns of the peppermill, and simmer for 1 to 2 minutes more, until most, but not all of the liquid has been absorbed. Remove the pan from the heat, and add the tomato, basil, and butter. Swirl the pan until the butter is melted, and serve at once.