Preheat oven to 300.F. Toss leeks with oil and salt.
Heat a large, oven-safe pan over medium-high heat. Place leeks cut-side down into the pan and leave undisturbed until golden-brown.
Cover pan and transfer to oven. Bake until leeks are golden and very tender.
Remove cover from leeks and broil until leeks begin to blister and slightly char.