In a pot, add pork belly and cook over medium heat for 2–3 minutes until the fat begins to render.
Stir in the kimchi and continue cooking for 5 minutes, allowing it to caramelize slightly.
Add the sliced onion and scallion whites. Sauté for another 2 minutes until fragrant.
Combine gochugaru, soy sauce, gochujang, garlic, and sugar.
Pour in sauce base and broth and bring to a simmer. Reduce heat to low and simmer for 10 minutes.
If using tofu, gently place cubes into the stew and simmer for another 5–10 minutes.
Finish with a drizzle of sesame oil and adjust seasoning to taste.
Serve bubbling hot with a bowl of steamed rice. Garnish with scallion greens and sesame seeds if desired.
