Heat the oven to 230 °C (210 °C fan) | 445 °F
Rinse the leeks thoroughly under running water, especially between the layers, to remove any grit and pat dry
Use a skewer or small knife to poke 5–6 holes lengthwise down each leek to let steam escape
Place the leeks directly on a baking tray without oil and roast for about 45 minutes, turning halfway, until the outer layers are black, burnt, and papery
While the leeks roast, mix all the ingredients for the Romesco sauce in a blender and blend until smooth and glossy
Take the leeks out of the oven, let them rest for 5 minutes, then peel away the burnt outer layers to reveal the soft insides and cut each leek in half
Spoon a round of Romesco onto each plate and spread it into a neat circle, then lay two half-leeks on top
Drizzle with extra virgin olive oil, squeeze over a little lemon juice, and finish with Maldon salt
