Preheat your oven to 200°C (390°F) and place an oven rack in the middle. Gather your ingredients and a baking sheet.
Trim the root ends of the leeks and remove any dark green tops or tough outer layers. Slice each leek lengthwise into halves or quarters, then rinse thoroughly under cold water to wash away any grit trapped between the layers. Pat them dry gently with a clean towel.
Lay the sliced leeks cut side up on the baking sheet in a single layer. Using a brush or spoon, drizzle generously with olive oil over the cut surfaces, ensuring they are well coated. Sprinkle with flaky sea salt and freshly ground black pepper for flavor.
Slide the baking sheet into the oven and roast for about 25 to 30 minutes. During this time, the leeks will turn golden at the edges and develop a smoky aroma. Check after 15 minutes and turn the sheet if necessary to promote even caramelization.
If the edges aren’t caramelized enough after 20 minutes, switch the oven to broil for 2 to 3 minutes, keeping a close eye to prevent burning. The leeks are ready when they’re tender, slightly charred, and fragrant with smoky sweetness.
Remove the baking sheet from the oven and let the leeks rest for 5 minutes. Squeeze fresh lemon juice over them for brightness, and drizzle with balsamic vinegar if you like a touch of tangy sweetness. Serve warm, garnished with herbs if desired.
