Bring to a simmer in a large skillet or Dutch oven over medium-high heat:
Add to the skillet, cut side down:
Reserve the leek greens for stock or discard. Reduce the heat to medium-low, cover, and simmer until very tender when pierced with a knife, about 15 minutes. Uncover, increase the heat to medium, and cook the leeks until golden brown and the liquid is almost gone, about 5 minutes. Meanwhile, melt in a small skillet over medium heat:
Add and cook, stirring frequently, until golden brown:
Transfer the leeks to a serving plate, cut side up, and top with the bread crumbs along with: