If you have some time, let the onions and black garlic fully caramelize. The sweetness they add to this spicy tofu soup is the perfect balance to the kick of heat. If you’re looking for a less spicy soup, reduce the gochujang.
Pearled barley soaks up so much of the flavor and cooking liquid, which is why I recommend it for this recipe. If you have hulled barley (with the bran on), it will take about 15 to 25 minutes longer to cook. You can reduce the cooking liquid by one third.
Swap the barley for brown rice. Check your soybean paste and chili paste for traces of gluten, which is listed in some brands. Gluten free miso is a good alternative with chili powder or your preferred chili paste.
Pork is the traditional meat served with Korean tofu soup (kimchi jjigae), on which this recipe is loosely based. I recommend browning your sliced meat with the onions and black garlic before adding water and barley.
Don’t have mizuna greens? Other Asian greens like bok choy, mustard greens or napa cabbage go well with this tofu soup. They will take a bit longer to cook, so add them with the tofu. Leafy greens such as dandelion greens, chard, or beet greens will cook similarly to the mizuna greens. These are also good options.
Likewise, you can easily substitute firm tofu for silken tofu depending on what you have.
Black garlic is a slow cooked garlic. You can typically find it at health food stores. If you don't have this ingredient, use regular garlic but add it after the onions are cooked. Alternately, use roasted garlic in place of the black garlic as the sweetness is similar.