Take the meat out of the fridge an hour before preparation so it can come to room temperature.
Preheat the oven to 80°C (176°F), sear the outside of the roulade till golden and place in the oven in a tray with the tomatoes, onions and celery. Cook for about 30-45 min to a core temperature of 58 degrees, take out and leave to rest in tinfoil. Make a gravy of the juice left in the oven tray.
Heat the oven to 200°C (392°F), peel the beetroots and cut into quarts, mix with some olive oil and roast for about 20-30 min, season with pepper and salt. Dress the beetroots on the plates with the roulade and garnish with the onions, celery, tomatoes and gravy. Grate some fresh horseraddish on the vegetables.
Enjoy your meal!