• Gather all the ingredients.
  

To Prepare the Mushrooms

• To rehydrate the shiitake, add 6 dried shiitake mushrooms and about 1 cup water to a bowl and let them soak for 30 minutes. Place a smaller bowl on top to keep the mushrooms submerged.
  
• When the shiitake are soft and tender, remove them from the soaking liquid and gently squeeze them out. Cut off and discard the stems. Then, cut the mushroom caps into very thin slices and squeeze out any remaining liquid.
  

To Cook

• Place the sliced shiitake in a saucepan. Add 1 cup dashi (Japanese soup stock), 1 Tbsp sake, and 1 Tbsp mirin.
  
• Add 1 Tbsp soy sauce and 1 Tbsp sugar and mix it all together.
  
• Cook over medium-low heat, then reduce the heat to a simmer and cook until the liquid reduces and is almost gone, about 20 minutes. Leave enough broth to just cover the mushrooms. Remove from the heat and let the mushrooms cool completely in the simmering broth to absorb more flavor.
  

To Serve and Store

• It's now ready to serve at room temperature, warm, or chilled. To chill, transfer the mushrooms and broth to an airtight container and store it in the refrigerator for 4–5 days. The flavor will improve the longer the mushrooms soak in the seasoned broth. You can also freeze it for up to 1 month. When you're ready to serve, defrost it in the refrigerator overnight. To serve it warm, bring it to a simmer in the saucepan.