Tonkotsu Broth
This broth takes some serious work and serious time (10-12 hours typically), however the results are well worth it, and also freeze quite nicely. I recommend making a big batch and saving the rest for a rainy day.
Place pork and chicken bones in a large stockpot, cover with cold water, and bring to a boil. Meanwhile, in a large sauté pan with a small amount of high-smoke point neutral oil, char onion and ginger (about a 4-inch knob, roughly chopped). Once the bones have reached a boil, drain all water and rinse bones thoroughly (extremely ?#@&ing thoroughly) under cold water to remove any brown bits remaining. Clean stock pot of any debris, and return bones to pot along with charred vegetables, leek, green onion, and garlic, as well as the pork fat back (if using). Cover all ingredients with cold water, plus an inch or two extra (remember you can always add more water if the stock over-reduces). Bring broth to a rolling boil, lower heat, cover, and let cook at a slow boil for 4 hours or until fat back is completely tender. Remove fat back and refrigerate, and continue to cook broth for another 6-8 hours, removing the lid the last hour so that the broth can reduce. Strain through a fine mesh sieve (optionally lined with cheesecloth) and reserve until ready to use. To serve, finely (essentially microscopically) mince the fat back and whisk into broth. Add toppings and enjoy.