Put the dried porcini in a bowl, cover with water, and soak for at least 15 minutes.
Put 1tablespoon of the butter and the vegetable oil in a skillet and place over medium-high heat. When the oil and butter are hot and the butter is just beginning to turn color, put in the veal medallions. Cook for 4 to 5 minutes on each side for medium doneness. Transfer to a platter and season with salt and pepper.
While the veal is cooking, thinly slice the white mushrooms.
After transferring the veal, coarsely chop the sage and add it to the skillet. Add the wine and let it boil for about 30 seconds to let the alcohol evaporate. Remove the pan from the heat.
Lift the porcini out of the water and squeeze the excess back into the bowl; do not discard the water. Rinse the mushrooms under running water, then coarsely chop them. Put the skillet back over medium-high heat and add the porcini along with the soaking water. Be aware that there may be some sand at the bottom of the bowl, so pour carefully or strain through a paper towel. Cook until the porcini water is almost completely evaporated. Add the fresh mushrooms, season with salt and pepper, and cook until the mushrooms are tender and all the liquid they release is evaporated, 10 to 15 minutes.
While the mushrooms are cooking, finely chop enough of the parsley leaves to measure 2tablespoons. When the mushrooms are done, add the parsley and the remaining 1tablespoon butter. Return the medallions to the pan and turn them in the sauce to heat them through. Serve at once.
This recipe is also very good with loin chops. To ensure they are done near the bone, let them cook in the sauce, covered, for 3 to 5 minutes before serving.