Fill a large pot halfway with oil and heat on medium-high.  Test the temperature of the oil by sprinkling a small amount of flour into it; when the oil foams or sizzles, it is ready to fry.
Cut the white base from leeks and discard.  Rinse the remainder and cut into small strips.  Place the strips in a large zip-locking plastic bag, add parsley, rosemary, and flour, and shake to coat evenly.
Remove leeks and herbs from bag, lower into oil, and fry until golden brown.  Transfer with a slotted spoon onto a paper towel and season with salt.
Can be used as a topping over meat or risotto.