Preheat the oven to 425 degrees. Prepare the leeks. Trim the root end of the leeks and trim the dark green ends, You want the white and light green sections. Cut the leeks in half lengthwise and rinse well to remove all dirt and debris. Dry well.
Bake for 30-35 minutes or until the leeks are beginning to brown and caramelize on the bottom. The exact cooking time depends on the thickness of the leeks. Smaller leeks may cook in 25 minutes and larger leeks may take 40-minutes. They should be tender and easily pierced with a fork.