Spanish-style romesco sauce is bright with red peppers, but rich with garlic and nuts. Drizzle it over everything to make a one-skillet chicken dinner even more enticing.
Allergen Note: Contains tree nuts.
Preheat the oven to 425°F.
To prep the leeks, trim the roots and remove the dark tops, reserving the white and pale green parts. Quarter or halve the leeks and cut them into 4- to 5-inch lengths. Rinse in cool water and pat or shake dry. Rinse and cut the potatoes into bite-size wedges. Combine the leeks and potatoes in a bowl, drizzle with 2 tablespoons olive oil, sprinkle with salt, and toss to coat.
Preheat a large cast-iron skillet or ovenproof pan over medium-high heat. Add the chicken thighs, skin-side down, and cook until the fat renders and the skin is lightly golden, about 5 minutes. Flip the chicken and add the potatoes and leeks to the pan, nestling them around the chicken. Transfer the pan to the oven and roast until the chicken is golden and no longer pink at the center, and the potatoes and leeks are tender, 35 to 40 minutes.
Transfer the chicken thighs to plates, and spoon the leeks and potatoes on the side. Stir the romesco, drizzle it over everything, and serve warm.