Preheat the oven to 200C/190C fan/Gas 6. Scrub the beetroot, carrots and Jerusalem artichokes. Cut the carrots in half lengthways. Cut the beetroot into small cubes. Cut the Jerusalem artichokes into 1 cm thick slices.
Toss the veg with 1 tbsp olive oil and plenty of seasoning. Tumble it in a single layer onto a baking tray. Slide into the oven to roast for 30 mins.
Peel and finely grate the horseradish. Whisk with 1 tbsp cider vinegar. Finely chop most of the tarragon leaves. Mix everything together with the creme fraiche and some seasoning.
Wrap the salmon in a piece of foil. When the veg has cooked for 30 mins, remove the tray from the oven. Scatter over the caraway seeds and 1 tbsp vinegar and toss everything together. Place the foil wrapped salmon on to the tray. Slide back into the oven for 10 mins.
Remove the tray from the oven. Divide the veg between two plates. Open the foil wrapped salmon. Flake it into large pieces and place on top of the veg. Serve with a good dollop of the horseradish cream. Scatter over the remaining tarragon leaves to serve.