Remove the meat from the fridge approx. 30 mins. prior to cooking. Preheat the oven to 80°C, warm the platter and plates. Heat the oil in a frying pan. Salt the meat, brown on all sides for approx. 5 mins., only turning when a crust has formed. Remove from the pan, roll in the peppercorns, place on the warmed platter. Insert the meat thermometer so that it does not touch the bone.
Cook at a low temperature for approx. 1 1/4 hrs. The core temperature should be approx. 55°C. The meat can then be kept warm at 60 °C for up to 30 mins.
Pour the stock into the pan, loosen any bits that have stuck to the pan, pour in the beetroot juice, stir the cornflour into the water and add to the pan while stirring, bring to the boil. Reduce the heat, simmer for approx. 5 mins., add the diced beetroot, heat gently, season with salt.
Heat the oil in a non-stick frying pan. Reduce the heat, fry the potatoes and rosemary for approx. 15 mins., turning occasionally, season with salt.