There's no simple way to make an authentic tonkotsu stock at home, it's very complicated. Instead, try this simpler recipe - it's not authentic but still super delicious!
White asparagus & juice (in a jar), Soya milk (or cow's milk), Egg (large), Miso (white), Salt, Chicken breast fillet and prawns, Thick sauce:, Asparagus juice (from the jar), Dashi broth, Light soy sauce, Mirin, Potato starch in a bit of water