Put pork belly in a bowl. Add garlic, ginger, soy sauce, sesame oil and fish sauce. Toss well to coat and let marinate for 10 minutes.
Step 2
Set a heavy-bottomed soup pot over medium heat. Melt butter, then add pork belly mixture and let it cook gently for 5 minutes. Add onion and cook, stirring, until softened, about 5 minutes. Turn heat to medium high and add kimchi, gochujang and gochugaru. Let mixture simmer for 2 minutes.
Step 3
Add kimchi juice and water (or broth, if using) and bring to a boil. Reduce heat to a brisk simmer and cook for 20 minutes. Taste broth and adjust seasoning.
Step 4
Just before serving, add tofu and stir gently to combine. When tofu is heated through, ladle into bowls and garnish with scallions.