The combination of potatoes and mushrooms is an Italian classic. Meaty, umami-packed fresh porcini foraged at the height of the season are the fungi of choice. But according to Colman Andrews in his book “The Country Cooking of Italy,” because porcini are expensive, some Italians stretch the mushrooms by cooking them with potatoes. We build on this idea to make a delicious skillet side with buttery Yukon Gold potatoes and mixture of dried porcini and fresh cremini (or portobello) mushrooms. We maximize the porcini flavor by using some of the water in which they are rehydrated as the braising liquid. A handful of fresh parsley and a splash of white balsamic vinegar, both added at the end, balance the deep, rich, earthiness of the dish.