Trim ends and sides of potatoes to form a rectangle. Cut potatoes into 1/4-inch sticks about 3 inches long. Put potatoes in bowl and cover with water. Heat about 3 inches of oil in large heavy pot to 325 degrees. Drain potatoes and dry thoroughly. Drop potatoes, about 1 cup at a time, into hot oil and fry for 5 to 6 minutes until tender and just starting to turn brown. Remove from oil with slotted spoon and drain on paper towels. Let cool. Heat oil to 375 degrees. Fry potatoes in batches as before for about 1 to 2 minutes until crisp and brown. Remove from oil with slotted spoon and drain on paper towels. Sprinkle with salt, if desired and serve immediately.