Add 1 cup of the broth and the soy sauce, and use a wooden spoon to scrape up any browned bits on the bottom of the pot. Add the remaining 3 cups of broth, increase the heat to medium-high and bring to a boil. Reduce the heat to medium-low and simmer for 10 minutes, so the flavors can meld.
Stir in the cabbage, then use a dinner spoon to break up the block of tofu and scoop the pieces into the soup. Cook until the cabbage is tender but not limp, 2 to 4 minutes. Taste, and stir in more doenjang and soy sauce, if desired. Ladle into bowls and serve hot.
Notes
I added an extra Tbls of doenjang and an extra tsp of soy sauce when adjusting the above recipe to my taste.