8 cups chicken broth
½ cup white miso
4 ounces shiitake mushrooms, stemmed and sliced thin
4 scallions, white and green parts separated, green parts sliced thin on bias
6 garlic cloves, smashed and peeled
1 (1½-inch) piece ginger, peeled and sliced into ½-inch-thick rounds
1 (2½-pound) boneless pork butt roast, trimmed
½ teaspoon pepper
1 (4-inch) square piece kombu (optional)
6 (3-ounce) packages ramen noodles, seasoning packets reserved for another use
Whisk broth and miso together in slow cooker. Add mushrooms, scallion whites, garlic, and ginger. Sprinkle pork with pepper and transfer to slow cooker. Cover and cook until pork is tender and registers 195 degrees, 4 to 6 hours on high or 8 to 10 hours on low. Transfer pork to cutting board and let rest for 20 minutes.
Meanwhile, add kombu, if using, to broth mixture in slow cooker and cook, covered, on high for 10 minutes. Using slotted spoon, remove and discard scallion whites, garlic, ginger, and kombu, leaving mushrooms in slow cooker.
Bring 4 quarts water to boil in large Dutch oven. Add noodles and cook until tender but still chewy. Drain noodles and divide evenly among serving bowls. Slice pork in half lengthwise, then slice crosswise ¼ inch thick. Ladle broth into bowls. Serve ramen topped with 3 or 4 slices of pork and scallion greens.