Coat the beetroot edges with egg white all round. Mix the remaining egg white with the salt. Transfer approx. 1/3 of this mixture to a baking tray lined with foil. Place the beetroot on top, cover with the remaining salt, press down well.
Bake for approx. 1 hr. in the lower half of an oven preheated to 200°C. Remove from the oven and allow to cool a little. Combine the crème fraîche, horseradish, lemon zest and juice, season with salt.