• Gather all the ingredients.
  
• If you cannot find sliced beef in your local grocery store, freeze a block of fresh chuck or rib eye for 1-2 hours and slice. See this post for detailed instructions. After you slice, if the piece is too large then cut them in half. I use "Komagire" cut from my local Japanese market and I cut them further into smaller pieces.
  
• Cut the onion into thinly slices and chop the green onion. Set aside.
  
• Heat a large frying pan over medium-high heat and add ½ cup (120 ml) dashi, 1 Tbsp sake, 1 Tbsp sugar, 2 Tbsp mirin, and 2 Tbsp soy sauce.
  
• Cover the lid and bring the sauce to boil. Once the sauce is boiling, add the sliced onions and spread them out. Cover to cook until tender (if you don’t cover, the sauce will evaporate, so make sure you cover the lid).
  
• When the onion is tender, add the beef and cook until no longer pink. Skim off the foam or fat with a fine-mesh sieve.
  
• Serve the meat and sauce over steamed rice.
  
• Top with chopped green onion and pickled red ginger. If you like to add an egg, serve with onsen tamago. Alternatively, you can pour beaten egg over the meat when it’s almost finished cooking in the pan (see how I do it in my other Gyudon recipe).
  

To Store

• You can keep the leftovers in an airtight container and store in the refrigerator for up to 3-4 days or in the freezer for a month.