Preheat your oven to 200°C (390°F). Line a baking sheet with parchment paper for easy cleanup.
Trim the dark green tops off the leeks, leaving about 4 inches of the tender white and pale green stalks. Rinse them thoroughly under cold water to remove any dirt trapped between the layers.
Slice each leek lengthwise in half, keeping the halves attached at the root end. This exposes the layers and allows for even roasting.
Arrange the leek halves cut-side up on the prepared baking sheet, spacing them evenly for proper heat circulation.
Drizzle the leeks generously with 3 tablespoons of good-quality olive oil, ensuring the cut sides are well coated to promote caramelization.
Sprinkle the leeks with flaky sea salt and freshly cracked black pepper. Tuck in a sprig of thyme or rosemary if using, for added aroma.
Place the baking sheet in the oven and roast the leeks for 30 to 40 minutes. Check halfway through and rotate if necessary. The leeks should be tender, golden, and slightly caramelized around the edges.
Once roasted, remove the leeks from the oven and let them rest for a few minutes. The aroma should be sweet and smoky, with crispy edges and soft centers.
Finish by zesting the lemon over the roasted leeks and squeezing a little fresh lemon juice for brightness. Drizzle with a little extra olive oil if desired.
Serve the roasted leeks warm or at room temperature, enjoying their sweet, smoky flavor and tender texture with each bite.
