Grate the cooked beetroot into a metal bowl.
Dry fry the fennel seeds and grind into a powder using a spice grinder.
Mix vinegar, sugar, garlic, ginger, and chilli with the fennel powder.
Boil the mixture for 20 minutes, pour it over the beetroot, and let it cool.
Boil the potatoes in their skins until soft, then peel them while warm.
Crush the potatoes and mix in wasabi, horseradish, egg yolks, and chives.
Heat an oiled pan and cook the potato mixture in oiled egg rings until golden on both sides.
Grill the oiled beef fillets for 3-4 minutes per side and let them rest.
Top a potato cake with sliced beef and the beetroot mixture to serve.