• Gather all the ingredients.
  

To Prepare the Ingredients

• Sprinkle Diamond Crystal kosher salt and freshly ground black pepper on both sides of 2 skin-on salmon fillets.
  
• Thinly slice ½ onion and cut 3 oz carrot into julienne strips.
  
• Cut off the bottoms of 1.8 oz shimeji mushrooms and 2 shiitake mushrooms. Separate the shimeji mushrooms by hand into small clusters. Thinly slice the shiitake caps.
  
• Cut 2 leaves chives into small pieces.
  

To Prepare the Foil Packets

• Prepare 2 sheets of aluminum foil, each 12 x 12 inches (30 x 30 cm). Divide ½ Tbsp unsalted butter and thinly spread it in the center of the foil sheets (reserve the remaining 1 Tbsp unsalted butter for later).
  
• For one foil packet, place one portion of the onion slices on the foil. Then, put one salmon fillet on top, skin side down.
  
• Top with one portion of the mushrooms and carrot julienne strips.
  
• Add ½ Tbsp sake and ½ Tbsp butter on top.
  
• Bring the top and bottom of the aluminum foil together over the salmon and fold a few times to close the top. Then, bring the sides together and fold a few times to tightly sealed the foil packet. Repeat the same process for the other fillet.
  

To Cook on the Stovetop

• Place the salmon foil packets in a frying pan and cover with a lid (no need to add water). Cook the salmon over medium heat for 2 minutes, then medium-low heat for 10 minutes. If your salmon is 1–1½ inches thick, cook for 15–18 minutes. Carefully open the foil packet (avoiding the hot steam) to check the doneness, if needed.
  

To Bake in the Oven (optional)

• Alternatively, you can bake in a preheated 425ºF (218ºC) oven for 15 minutes. For a convection oven, reduce the cooking temperature by 25ºF (15ºC). If your salmon is 1–1½ inches thick, bake for 18–20 minutes. Carefully open the foil to check the doneness.
  

To Serve

• Carefully open the foil packets, avoiding the hot steam. Sprinkle with the chopped chives and drizzle each with 1 Tbsp ponzu or soy sauce. Enjoy!
  

To Store

• You can keep the leftovers in an airtight container and store in the refrigerator for up to 3 days and in the freezer for 2 weeks.