Cut the french fries with mandoline or french fry cutter 1/4-inch strips. Heat a saucepan or stock pot (at least 2 gallon capacity) with the oil about 250 degrees (use a thermometer to gauge). Add the french fries and cook, stirring to avoid clumping together, about 3 minutes, until soft but not mushy. Remove with a mesh strainer and drain onto paper towels. Turn heat to high and heat oil to 350 degrees. At the last minute before serving plunge the fries into the oil and cook until golden brown. Remove from oil, drain onto towels and season with salt to taste.