Use a food processor to grate the peeled potatoes.  Put the grated potatoes in ice water and refrigerate. 30 minutes before eating remove the potatoes from the refrigerator and drain in a colander.  Lightly salt and toss the shredded potatoes.  Heat olive oil and butter in a skillet over medium-low heat.  When hot, divide the potatoes into 4 piles in the skillet, careful that they don’t touch. Cook slowly until well browned (about 7 minutes).  Flip and cook on the other side until it is browned also (another 7 minutes).  Adjust the time and heat to get the right amount of “browned.”