Wash leeks thoroughly and remove their leafy greens and about ½” inch off the bottom of each stalk. Chop in half vertically.
Place a baking sheet in the oven and preheat to 400º.
In a large bowl, toss leeks with olive oil and salt until well-coated. Place leeks onto preheated baking sheet, cut side down. Carefully wrap the baking sheet in foil – you don’t have to seal it completely closed, but as tightly as possible is good. Return sheet to oven and decrease heat to 300º.
Bake for 1:15 to 1:30, until leeks are very tender. Remove sheet from oven and flip the leeks. Return to oven, increase the heat to 400º and cook for 15-20 minutes until they are crispy and golden brown.