To make the ramen broth, place the pork bones in a large pot and cover with cold water. Set over a high heat and bring to the boil. Boil for 10 minutes so all the impurities in the bones rise to the top of the pot.
Rinse the bones under the cold faucet, and transfer them to an Instant Pot, along with the aromatics. Cover with enough cold water to fully submerge the bones, up to the maximum fill line. Secure the lid and set to pressure cook on high for 80 minutes.
Allow the pressure to naturally release. Then, set the Instant Pot to sauté on high with the lid off, reducing the broth until you have approximately 6 cups, and the broth is rich and milky.
Meanwhile, roast the pork. Pre-heat the oven to 390F and season the pork all over with salt. Place in a baking dish and roast for 1 hour, reducing the heat to 320F after 30 minutes. Set the meat aside to rest on a plate covered with foil that will collect the resting juices for 30 minutes.
To make the ramen tare, combine the miso, mirin and sake together in a small pan until you have a smooth paste. Set over a medium high heat and allow to come to the boil, stirring regularly, to cook off the alcohol in the mirin and sake. Remove from the heat and set aside. Thinly slice the pork before adding the resting juices to the ramen broth.
To serve, divide the ramen tare between 4 bowls, and add a ladle of the ramen broth to each. Whisk, so the paste combines with the broth, before adding dividing the noodles and pak choi between each bowl. Divide the rest of the broth between the bowls before adding the rest of the toppings and a few slices of the roast pork. Serve with soy sauce on the table for anyone who wants to adjust the seasoning.