Combine cold water and kombu in a medium saucepan; bring to a simmer over medium heat. Stir in bonito flakes and remove from heat; let stand for 5 minutes. Strain out solids using a fine mesh strainer, discarding them or reserving for a second use.
Add pork broth, chicken broth, and ginger to the saucepan with the liquid (dashi). Set a sieve just below the broth's surface and add both miso pastes to it; use the back of a spoon to work the miso through the sieve, dispersing it into the broth. Over medium heat, cook and stir until the mixture comes to a simmer. Remove from heat.
To Make the Eggs
Meanwhile, prepare an ice bath for the eggs.
Fill a small saucepan with enough water to cover eggs and bring to boil over high heat. Reduce heat to medium and slowly lower eggs into boiling water with a slotted spoon (to avoid cracking). Reduce heat to simmer and cook 7 minutes (or longer if you prefer firmer yolks); transfer eggs to ice bath for 5 minutes or more.
To Prepare the Pork Belly
Cut the Oven Roasted Crispy Pork Belly (or other cooked pork belly) into lengthwise slices, about 1/8-inch thick. In a skillet over medium heat, fry the slices until the edges become crisp, approximately 5 minutes. Remove from heat.
For the Ramen Bowls
Place miso broth back over medium-high heat and bring to boil.
Add ramen noodles to boiling broth and cook 2 minutes. add bok choy; bring to boil and cook 1 to 2 minutes more, or until noodles are tender.
Divide ramen between 4 bowls. Top each with two egg halves, 1/4 of pork belly and garnish as desired with seasoned oils, green onions, nori, and seasonings. Serve.
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Notes
You can find bonito flakes (shaved katsuobushi: simmered, smoked and fermented skipjack tuna) and dried kombu online and in the Asian food section of many large grocery stores.
For spicy miso ramen, you may want to use 2 tablespoons or more of the chili oil.