Nikomi Hambagu (煮込みハンバーグ) is the hambāgu that’s simmered (in Japanese, the word is nikomu) in the sauce. After searing the patties, they are cooked in the savory wine-reduction sauce until the patties are fully cooked through and absorb all the flavors from the sauce.
Restaurants usually make demi-glace sauce from scratch, using vegetables and flavorful stock. However, at home, we would make a quick sauce with common condiments like ketchup, Worcestershire sauce, and wine.
Cook the onion and mushrooms and make the hambagu sauce. Place the unwrapped Hambagu with demi-glace sauce in boiling water for 10 minutes. Put the patties into the sauce and let it simmer for 5 minutes. Optionally, put the cheese on top to melt. Serve with steamed broccoli and baked potato fries.