• Gather all the ingredients.
  

To Prepare the Kombu Dashi

• Remove any dust or particles on kombu with a damp cloth (but leave the white powdery substances which contribute to the umami flavor in the stock). These days kombu is much cleaner and you don‘t really have to wipe it. Never wash it under running water!
  
• In a donabe (Japanese clay pot), put 1 piece kombu (dried kelp) and 1½–2 cups water. Let the kombu soak for 1–2 hours. If you‘re short on time, you can steep the water with kombu slowly over the lowest heat.
  

To Prepare the Sauce

• Meanwhile, make the sauce. To a small saucepan, add ¼ cup soy sauce, 1 Tbsp sake, and 1 tsp mirin.
  
• When boiling, add ½ cup katsuobushi (dried bonito flakes).
  
• Mix well with chopsticks and cook for 1–2 minutes.
  
• Pour the sauce into a small serving dish. You don’t have to strain it; it’s okay if some bonito flakes go into the sauce.
  
• These leftover bonito flakes have a nice flavor and you can use it as filling for Okaka Onigiri or to make Homemade Furikake (rice seasoning).
  

To Prepare the Hot Tofu

• When the kombu dashi is ready (after 1–2 hours), bring the dashi to a boil on medium heat. If you were slowly heating up the kombu dashi (because you didn‘t have time to soak for 1–2 hours), bring it to a boil, too. Once boiling, add 1 Tbsp sake and ¼ tsp Diamond Crystal kosher salt.
  
• When boiling again, cut 1 medium-firm tofu (momen dofu) to any size you like (whole tofu, halves, or 6 pieces, for example) and put it in the kombu dashi.
  
• When the tofu is heated through, after several minutes, add the mitsuba (Japanese parsley). If you plan to use other vegetables, make sure are they cooked through.
  
• While the tofu is hot, serve it with the sauce and add the optional toppings of your choice, such as chopped green onion/scallion, grated ginger, shichimi togarashi (Japanese seven spice) and yuzu kosho (Japanese citrus chili paste).