Cut off the dryer green parts of the top and the roots on the bottom and throw them away. Then slice the leek in half, lengthwise. Leeks generally have dirt and bugs between the leaves, so clean the pieces really well, one by one, under running water.
Shake off excess water and gather the leaves together to cut them into small quarter-inch pieces. Then transfer to a pot, and add one cup of water and ½ tablespoon salt. Boil for about 5-7 minutes. The smell of the leek will become milder as they cook.
Drain the leek in a sieve and set aside.
Peel, dice, and boil the potatoes in salt water for about 15 minutes or until soft. Then drain the potatoes.
Combine the potatoes and leek in a bowl and mash with a potato masher. If you prefer a smoother texture, you can also mix them in a blender or food processor.
Add egg, pepper and ½ cup breadcrumbs to the leek mixture. The batter should be thick and not stick to the fingers.
Pour remaining ¼ cup breadcrumbs onto a plate. Take golf ball-sized portions of batter and flatten them into patties by hand. Coat them in the crumbs from both sides.
Pour oil into the pan until it covers about ¼ inch of the surface. Heat until small bubbles form and set to medium heat. Fry patties on both sides for about five minutes, or until brown.
Remove from oil and let the patties cool down on a paper-towel-covered plate. Once cool, transfer to a serving plate and throw the paper away.
Enjoy your Kefte De Prasa! Hanukkah sameach!