The ratio of soy sauce and mirin is 1:1. It's easy, but it transforms cheap maguro (lean tuna) into something delicious. Try topping it on a rice bowl.
I wanted to transform a cheap cut of maguro delicious.
After bringing the soy sauce and mirin to a boil, make sure to cool it down. Use hon-mirin. You can make this with mirin seasoning, but hon-mirin tastes better.
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