Heat the oven to 220°C / 200°C fan. Scrub the potatoes and cut into 2–3 cm pieces. Boil in water for 5 minutes, drain well and let them steam dry for 5 minutes.

Toss the potatoes with 35 ml of the olive oil and ½ teaspoon salt. Spread on a large tray in one layer. Roast for 30–40 minutes, turning halfway, until crisp outside and soft in the centre.

Meanwhile, peel and finely chop the onion and garlic, and chop the tomatoes. Heat the remaining oil in a saucepan. Soften the onion for 8–10 minutes, then stir in the garlic, paprika and chilli for 30 seconds.

Immediately add the tomatoes, tomato purée, 100 ml tap water and the remaining salt. Simmer for 20 minutes, stirring, until thick. Stir in the sherry vinegar. Remove from the heat and carefully blend smooth, or leave a little texture if preferred.

Spoon the hot bravas sauce over the potatoes just before serving and scatter with washed, chopped parsley. Serve straight away while the potatoes are crisp.