Marinate the pork belly with the garlic, ginger, gukganjang and soju while you prepare the other ingredients.
Heat a heavy bottomed pot until hot and then add the pork belly. Allow some of the fat to render out of the pork belly, then add the onions and kimchi. Sauté until the mixture is very fragrant.
Add the kimchi juice, water, gochujang, and doengjang, stirring everything together to combine.
Bring to a boil and taste for spiciness, adjust with gochugaru to increase the heat to where you want it.
Add the tofu, turn down the heat to a simmer and let it cook for 15-20 minutes, or until the pork and kimchi are tender.
When you're ready to serve the kimchi jjigae, add the green onions and butter and give it a quick stir to incorporate. Put a trivet on the table and serve it straight out of the pot along with a bowl of rice.