Heat the oven to 400°F. Rinse and trim the bottom of the cauliflower. Stabilize the head with the flat side on a cutting board and carefully cut downward in half. Put 1/2 cup water and 1 tablespoon oil in a medium skillet. Add the cauliflower, sprinkle with salt and pepper, turn the heat to medium-high, and cover. Cook, peeking occasionally, until the wedges are fork-tender, 5 to 10 minutes. Remove the lid and continue cooking, undisturbed until the water evaporates, and the cauliflower edges are crisp and brown on one side, 2 to 5 minutes.
Scrub and halve the potatoes. Put them on a medium rimmed baking sheet and drizzle with 2 tablespoons olive oil and half the Maldon’s salt and pepper and toss. Roast until brown and crisp in places, 15 to 20 minutes. Remove the pan from the oven and sprinkle with the remaining Maldon’s salt.
Chop the garlic. Put the almonds and garlic in a small skillet with the remaining tablespoon oil and over medium heat, and cook, stirring occasionally, until fragrant, 2 or 3 minutes. Rinse and drain the peppers in a colander. Put them in a food processor with the almond mixture, the vinegar, and a sprinkle of salt and pepper. Pulse until the sauce is as coarse or as smooth as you like; to thin it, add water, 1 tablespoon at a time as you work.
Transfer the Romesco back to the small skillet and warm over medium heat. Taste and adjust the seasoning. Rinse, trim, and chop the parsley. Slice the green olives.
To serve, put a small amount of the Romesco on a plate and top with a cauliflower wedge and the potatoes, Garnish with the sliced green olives and parsley.