Boiling potatoes briefly before roasting them, a restaurant technique, creates an outrageously crunchy crust. More Potato Recipes
Preheat the oven to 425°. Put the anchos in a heatproof bowl and cover with the boiling water. Set a small plate on top to keep the anchos submerged and let soak until softened, about 20 minutes. Discard the soaking liquid, stems and seeds and chop the anchos.
Meanwhile, in a large, heavy pot, cover the potatoes with water and bring to a boil. Add a large pinch of salt and cook over moderately high heat until just tender when pierced with a knife, about 25 minutes. Drain and let cool slightly, then peel the potatoes and cut into wedges. Transfer the potatoes to 2 large rimmed baking sheets. Drizzle with 1/4 cup plus 2 tablespoons of the olive oil, turn to coat and season with salt and pepper.
Roast the potatoes on the upper and lower racks of the oven for 40 minutes, switching the pans once, until the potatoes are browned and crisp.
Meanwhile, in a large skillet, heat the remaining 1/4 cup plus 2 tablespoons of olive oil. Add the chopped almonds and cook over moderate heat, shaking the skillet a few times, until lightly browned, about 4 minutes. Add the bread crumbs and cook until lightly toasted, about 1 minute. Let cool slightly, then transfer to a food processor. Add the anchos, piquillos, garlic, tomato, parsley and vinegar and process to a coarse paste; season with salt and pepper. Spoon the romesco sauce over the potatoes, sprinkle the olives on top and serve.
The potatoes can be roasted earlier in the day and reheated in a 400° oven before topping with the romesco sauce and serving. The romesco can be refrigerated overnight.