Dried porcini add a unique dimension to this classic sauce. Put 1 ounce dried porcini in a bowl, cover with water, and soak for at least 15 minutes. Lift the porcini out of the water and squeeze the excess back into the bowl; do not discard the soaking water. Rinse the reconstituted mushrooms under running water, then coarsely chop. When you add the tomatoes, add the mushrooms along with the water in which they soaked. Be aware that there may be some sand at the bottom of the bowl, so pour carefully or strain through a paper towel.