Peel and shred 4 cups( measured)of potatoes. Rinse, drain and pat dry, then mix the potatoes and onion together. Sprinkle the salt and pepper onto potatoes and mix. Heat the butter in a 10-inch skillet until melted. Put potato mixture firmly in skillet, leaving 1/2-inch space around edge.Cook over medium-low heat for approximately 15 minutes or until bottom is browned. Cut potato mixture into quarters and then turn them over.You may leave the potato mixture in one piece if you prefer. Place a large plate over skillet and invert potatoes onto plate. Slide potatoes back into skillet. Add 1 tablespoon of butter if needed. Cook about 12-14 minutes longer or until bottom is brown. SERVES 4.