Preheat the oven to 200°C/400°F/gas mark 6.
Put the unpeeled, raw beetroot into a roasting tray with the thyme sprigs, 2 tablespoons of olive oil, a few pinches of salt and a few tablespoons of water. Cover with foil and roast for 1½–2 hours, or until a knife inserted through the middle meets no resistance.
Remove and allow to cool slightly before slipping off their skins.
Meanwhile cook your soft-boiled eggs.
Cut the beetroot into wedges and put them in a bowl with the spring onions, capers and herbs.
Mix the sour cream with the vinegar and remaining oil, season well and then stir into the beetroot.
Arrange the beetroot salad on a serving dish. Carefully peel the eggs, halve them lengthways and arrange on top.