Place potatoes in a large pot of salted water. Bring to a boil and cook 25 minutes or until tender. Drain and cool completely. Meanwhile, cook onions in oil in a saute pan over medium heat or until caramelized.. Stir occasionally. Cut potatoes in half and scoop out pulp with a melon baller, leaving a sturdy wall. Mas potato pul and fold into sour cream, salt and pepper. Fill potatoes with mixture and top with onions. Serve at room temperature.
*** to serve hot, place in oven at 350 degrees for ten minutes.