Make a quick stock: in a medium pot combine Dried Kelp and Dried Anchovies with Water, bring to a gentle simmer for 10–15 minutes, then strain to yield a clear Anchovy-Kelp Stock. (If you have ready-made anchovy-kelp stock, you may skip the simmer step.)
Prepare the ingredients: thinly slice the Pork Belly, roughly chop the Napa Cabbage Kimchi and reserve any Kimchi Juice, cut the Firm Tofu into bite-sized cubes, slice the Yellow Onion, thinly slice the Scallions, and mince the Garlic.
Heat a heavy pot over medium-high heat and add the sliced Pork Belly. Cook until the fat renders and the edges are lightly browned, about 4–6 minutes.
Add the chopped Napa Cabbage Kimchi to the pork and sauté until the kimchi softens and begins to caramelize, about 5 minutes. Stir in a tablespoon of Gochujang, a teaspoon (or to taste) of Gochugaru, and a pinch of Sugar to balance the acidity; add the minced Garlic and a splash of Guk-ganjang for depth, and cook 1–2 minutes to bloom the flavors.
Pour in the reserved Kimchi Juice and enough warm Anchovy-Kelp Stock to cover the ingredients (about 3–4 cups), bring to a boil, then reduce to a gentle simmer. Cook uncovered for 15–20 minutes so the flavors meld and the pork becomes tender.
Gently add the Firm Tofu cubes and sliced Yellow Onion to the stew and simmer 5–7 more minutes until the tofu is heated through and the onion is just tender.
Taste and finish: adjust seasoning with Salt, a grind of Ground Black Pepper, and more Guk-ganjang or Gochugaru if you want extra heat. Stir in the sliced Scallions just before serving.
Ladle the kimchi jjigae into bowls and serve piping hot with steamed rice and banchan for a classic, satisfying meal.
