If you can't find the spicy chili bean paste (la doubanjiang/toban djan/douban), you could use 1 1/2 tbsp white miso paste and about 1/2 tbsp spicy chili paste like gochuchang or sriracha. Adjust amounts to your own personal taste preferences. The fermented beans in the doubanjiang or miso will give the broth an umami flavor that you won't achieve otherwise.