Place veal between layers of wax paper and pound with a mallet until 1/4" thick. Sprinkle with salt and peppr then lightly dip into flour, shaking off excess. In a large skillet, melt 2 Tb. butter and the oil together. When butter is hot and beginning to lightly brown, sauté a single layer of veal. Brown for 2 to 3 minutes on each side and remove to a platter and keep warm. Brown remaining veal. When all the veal has been browned and removed, pour off all but a light film of fat and add the Madeira wine, lemon juice and broth, stirring and scraping up browned particles from the bottom of the pan. Mix cornstarch with the water until smooth. Add slowly to the wine-broth sauce and whisk until slightly thickened. Add the sliced mushrooms and simmer until bubbly. Arrange the veal slices on individual plates and top with a generous spoonful of the sauce and serve at once.