Preheat the oven to 200°C.
Peel the parsnips and carrots, chopping them into six pieces lengthways and removing the parsnip cores.
Peel and quarter the beetroot.
Heat 15ml of olive oil in a pan and fry parsnips and carrots for two minutes until coloured.
Add seasoning, butter, garlic, and thyme, then fry for six minutes until tender.
Stir in beetroot, honey, and vinegar to warm through, then set aside.
Roast walnuts for five minutes, then rub off the skins with a cloth.
Grind walnuts with garlic and 50ml of olive oil into a paste, seasoning with lemon juice.
Whisk crème fraîche, mustard, horseradish, and lemon juice into a dressing.
Spread the paste on plates, top with vegetables, watercress, and the dressing.