If you’re using the caraway seeds, dry-toast in a hot pan for 30 seconds. Crush and set aside.
If the beetroot comes with the tops (greens), remove, wash, then blanch for a minute. Drain and set aside.
Preheat the oven to 220C/fan200C/gas 7. Put the beetroot in a baking tray and toss with half the oil and a little salt. Roast for 20 minutes, until cooked through. When cooled slightly, put on clean rubber gloves and rub the beetroot skins off.
Whisk the remaining oil, vinegar, mustard, seeds and sea salt, then toss with the beetroot tops and roots. Serve cold.