Preheat oven to 180C. Peel 1.5kg Sebago or Coliban potatoes, cut into 5cm chunks. Partially boil for 10 minutes. Drain well, shake pan to rough up surface of potatoes. Heat 1/4 cup olive oil in a large roasting dish (in oven). Add potatoes, toss to coat, roast for about 1 1/2 hours, turning once, until golden brown and crisp.