For the black radish salad with beets and roast beef, first coat Beiried with pepper and mustard and sear on each side in a hot pan. Place on a wire rack and cook in a preheated oven at 180 °C (top/bottom heat) for 10 minutes. Then let cool and cut into thin strips. Alternative: Cook at 120 °C up to 54 °C core temperature.
Peel and finely grate black radish. Marinate with salt and apple cider vinegar and let stand for 5 minutes. Squeeze out and mix with sour cream and chives. Peel beets and cut lengthwise into thin strips with a peeler. Season with a little salt and pepper, mix well (keeping the beets separate) and let sit for about 30 minutes.
Mix all ingredients for the dressing well and season with salt and pepper. Toss beets, apple slices, nuts and the radishes well with the dressing. Arrange black radish in ring shapes (cookie cutters) on a plate, place beets on top and finish with roast beef.
Serve black radish salad with beets and roast beef right away.