Slice leek from the bottom [white] part to where the stalk becomes light / medium green in 3/8" to 1/2" rings. Carefully separate them into separate rings, discarding the tight, white centers.
Immerse rings in ice water and clean carefully. Remove, drain and carefully pat dry.
"Dredge" rings in cornstarch. Set aside.
Preheat peanut oil to 375 degrees.
Place flour in a bowl and whisk in milk. Add grated shallot. The batter should be the consistency of thin pancake batter. When you've achieved this, whisk in remaining ingredients.
Coat leek rings [in small batches] with the batter. Shake of excess and drop in oil and fry until deep, golden brown. Drain and sprinkle with sea or kosher salt while hot. Repeat steps until all rings are complete.
Fantastic on their own as a side dish, but equally as delicious on a burger, in a salad, or as a topping for soup. Enjoy!