Place the potatoes in a saucepan, cover with water and season with salt. Over medium heat, bring the water to a boil, reduce the heat to medium low and cook until the potatoes are tender. Remove from the water and cool completely. Peel the potatoes and pass through a coarse grater. In a large non-stick saute pan, over medium heat, melt the butter. Add the leeks. Season with salt and white pepper. Saute for 2 minutes. Add the potatoes and mix thoroughly. Using the back on a wooden spoon press the potato mixture firmly into the pan. Reduce the heat to low and cook until the potatoes are crispy and golden brown. Using a spatula, flip the potato cake over and continue cooking the other side. **Add more butter if needed. Remove from the pan and slice into individual servings.