Wash the beetroot well, dry it, wrap it in foil and bake at 80ºС for 2–2.5 hours. Cool in foil, peel and cut into slices 2–3 mm thick. Beat the butter with a whisk with passion fruit juice until an emulsion is obtained (you can add a little salt). Put the beets on a plate, pour over the emulsion and melted chocolate in a water bath, garnish with watercress.