1. Prepare Bones: Blanch pork bones in boiling water for 15-20 minutes to remove impurities. Drain and thoroughly rinse bones under cold water, scraping off any remaining scum or blood. This step is crucial for a clean broth.

2. Cook Broth (Pressure Cooker Method): Place blanched bones, pork fat (if using), sliced ginger, garlic, and green onion whites into a large pressure cooker. Add 5 liters of water, ensuring bones are covered. Lock the lid and cook on high pressure for 2-3 hours.

3. Cook Broth (Traditional Simmer Method): Place blanched bones, pork fat (if using), sliced ginger, garlic, and green onion whites into a very large stockpot. Add 5 liters of water, ensuring bones are covered. Bring to a rolling boil, then reduce heat slightly to maintain a vigorous, rolling simmer. Skim off any foam that rises. Continue to simmer for 10-18 hours, replenishing water as needed to keep bones submerged, until broth is milky white and opaque.

4. Strain Broth: Carefully strain the broth through a fine-mesh sieve, discarding all solids. If desired, you can pass it through cheesecloth for an even clearer (though still opaque) result. Season with sake, mirin, and soy sauce to taste.

5. Prepare Toppings: While the broth cooks, prepare your desired toppings, such as chashu, ajitama eggs, and slice scallions.

6. Assemble Ramen: To serve, warm your ramen bowls. Add about 2 tablespoons of tare (shio or shoyu) to each bowl. Ladle hot Tonkotsu broth over the tare and stir well. Cook ramen noodles according to package instructions until al dente. Drain well and add to the broth. Arrange chashu, ajitama egg, scallions, and nori artfully on top. Serve immediately.