In a small saucepan, mirin, sake, and sugar. Turn on the heat to medium and whisk all the ingredients together.

Then add soy sauce and bring to a boil. Once boiling, reduce the heat to low and continue simmering for 20-25 minutes. Toward the end of cooking, you will see more bubbles. Take off heat when temperature reaches 233. Immediately remove to a receptacle that can be immersed in an ice bath or place the entire pan in an ice bath.

Store in refrigerator. Sauce will thicken when cold.

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