You will be preparing your broth in advance, as it will take 12 hours to make. This is a great time to also begin to marinate your pork belly.
To marinate pork belly: combine soy sauce, mirin, cooking sake, sugar, garlic and green onions in a large freezer bag. You will sous vide the pork belly, so use a straw to suck the air from the back after you place the pork belly inside and massage the marinade into the meat. Make sure you create a vacuum seal around the meat.
Sous vide the pork at 160 F for 12 hours. This will be happening alongside the cooking of your broth.
Now, prepare your broth by blanching the bones. In a large stockpot, submerge pork and chicken bones in cold water. Bring the water to a rolling boil on high heat. Remove the bones once the boil begins.
During step 4, heat your cooking oil in a skillet on high heat. Add onions, garlic, and ginger. Cook until charred, anywhere from 13-16 minutes. Save for later.
Dump all the boiled water from the pot after removing the bones. Run the bones under cold water, using your fingers or a small instrument to remove any imperfections from the bones– marrow, blood, etc. Scrub the bones so they are white.
Back in the large stock pot, put bones, vegetables, leeks, scallions, pork fatback, and mushrooms. Cover with water and put on high heat, bringing to a rolling boil. Keep at a rolling boil for 30 minutes, using this time to remove any imperfections that float to the top of the broth.
Reduce to a soft boil and cover with a lid. After about 4 hours at this boil, remove the pork fat and reserve it in a Tupperware. Refrigerate for later. Continue cooking for another 7-8 hours, checking occasionally to ensure the broth is becoming opaque and creamy.
After 11-12 hours of cook time, bring the burner to high until the broth begins to reduce. Let it reduce until the broth has reached your desired consistency. Pass through a strainer into a clean pot, throwing out the solids used to flavor the broth. While the broth is reducing, get started on preparing your other ingredients for assembly.
Remove your pork from the vacuum-sealed bag and let it cool. Slice into thin slices, similar to bacon, and set aside.
Combine all the ingredients for the miso tare and simmer for 3-5 minutes.
Boil your eggs for 7 minutes, to achieve a soft-boiled yolk. Peel and slice in half lengthwise.
Now, begin to assemble your bowl. Cook the ramen noodles according to the package.
Fry the pork belly on both sides until lightly browned. Saute the mushrooms until soft.
Gather 4 bowls and equally distribute the miso tare into each bowl. Add broth into the bowls, and then the cooked noodles. Add in the boiled egg and top with green onions.
Add more toppings as you see fit, such as chili oil or bean sprouts. Enjoy!