01 -
Fill a large, shallow pot (about 12 inches wide) halfway with water and add 2 teaspoons of salt for every 2 quarts. Bring it to a boil. While waiting, rinse any visible dirt off the leeks. Poke a knife just below where the leaves begin and slice upward to the tips, leaving the main portion whole. Hold the leaves under running water to remove any dirt inside. Trim the roots closely and cut the dark green tops, leaving 1-3 inches.
02 -
Carefully drop the cleaned leeks into the boiling water. Let it come back to a gentle simmer, then turn the heat down to keep it steady. Cook for 8 to 10 minutes, or until you can slide a knife through the thickest part. Around 8 minutes, leeks about an inch thick will turn a slight olive-green color. If they're bigger, they might need extra time.
03 -
Use a pair of tongs to move the cooked leeks straight into an ice bath to stop them from cooking further. Let them cool completely.
04 -
Take the leeks out of the icy water with care. Lay them at a slight tilt in a rimmed roasting dish to allow any excess water to drain off. Leave them undisturbed for about 10 minutes while you mix up the dressing.
05 -
In a jar, blend together red wine vinegar, olive oil, mustard, black pepper, and kosher salt. Shake or whisk until everything combines well and the dressing emulsifies.
06 -
Arrange the leeks in a long-serving dish with sides. Pour the dressing all over them, turning the leeks gently to coat both sides. Cover the dish with plastic wrap and pop it in the fridge for a couple of hours, or up to 3 days. The longer they sit, the more flavor they pick up. They're best served after reaching room temperature.