6–12 h · hands-off
The night before, or at least 6 hours before cooking, soak and in water in a cold, non-reactive vessel. I use a big Tupperware container. (Technically this is optional, but I find the resulting tonkotsu is whiter in appearance.)
When ready to cook, add your neck bones and femurs to a pot with fresh water. Bring to a boil, then down to a simmer, and skim the scum that rises to the top of the pot. Do this for 15-20 minutes, or until little scum is rising. The scum goes through several phases here; you'll know when the scum is pretty much done rising. This blanch is integral for a white tonkotsu: don't skip it, and don't end it prematurely.
Strain the bones from the blanching liquid and discard the liquid. Scrub and clean the bones under running water, removing any black or dirty looking particulate that may be on the outside of the bones or in crevices.
Add your now clean bones to a pot with water 1.2 l (and backfat 100 g, if using, for extra fat). Cook at a medium boil for 18 hours, stirring frequently.
If using, add the aromatics (onion ¼ pc and garlic 2 pcs) to the broth in the last hour.
Strain the soup.
To finalize the emulsion, add the soup to a blender and blend on high for 30 seconds, being careful to gradually bring the blender to high to avoid splashing yourself, as the soup will rapidly expand when it blends. You can also use a hand blender, blending for 5 minutes, though the emulsion won't be as strong. Reserve the soup as needed.
