Step 1: Blanch the pork bones. Place pork trotters and neck bones in a very large stockpot. Cover with cold water and bring to a rolling boil over high heat. Boil for 10-15 minutes, skimming off any foam or impurities that rise to the surface. This step is crucial for a clean broth.
Step 2: Clean the bones. Drain the blanched bones in a colander. Rinse each bone thoroughly under cold running water, scrubbing off any remaining gray scum or blood. Clean the pot as well.
Step 3: Start the long simmer. Return the cleaned pork bones and chicken carcasses (if using) to the large, clean stockpot. Add the quartered onion, halved garlic head, sliced ginger, and roughly chopped green onions. Cover everything with at least 4-5 inches of cold water (about 5-6 liters).
Step 4: Boil and reduce to a rolling simmer. Bring the pot to a high boil over high heat. Once boiling rapidly, reduce the heat to maintain a strong, rolling simmer. The surface of the water should be actively bubbling. Do not cover the pot entirely; leave a slight gap for steam to escape.
Step 5: Skim and replenish. Throughout the simmering process (which will be 8-12 hours), regularly skim off any fat or impurities that rise to the surface. As the water evaporates, replenish the pot with hot water to keep the bones fully submerged. This constant attention is key to achieving a rich, milky broth.
Step 6: Add umami boosters. About 30-60 minutes before the end of the cooking time, add the dried kombu and dried shiitake mushrooms. Do not add them earlier, as overcooking kombu can result in a bitter or slimy broth. After 30-60 minutes, remove and discard the kombu and shiitake.
Step 7: Strain the broth. Once the broth has simmered for 8-12 hours and has turned a milky white color, carefully strain it through a fine-mesh sieve or a cheesecloth-lined colander into a clean container. Press on the solids to extract as much liquid as possible. Discard all solids. Your rich, delicious ramen broth is now ready. Taste and add a pinch of salt if desired, but remember the tare will provide most of the seasoning.