• Mix ingredients together. I advise making twice or triple the quantity for Yaki Onigiri or other unagi recipes since the unagi sauce may be stored for three months.

How to Prepare the Unagi Sauce

• Mirin, sake, sugar, and a small pot should be used.
• After combining the ingredients, place the pot on the stovetop at medium heat. Bring the mixture to a boil after adding the soy sauce.
• After boiling, lower the heat to maintain a medium simmer; you should notice little bubbles around the pan's edge. Simmer for another 10-15 minutes, or until the liquid is reduced to about one-third of its initial volume.
• Once the sauce finishes boiling, it will thicken and start to bubble more. Verify that the sauce has thickened to a third of its original consistency using the chopstick. After that, take it out of the heat. The sauce will thicken more as it cools.
• Remove the unagi
• To fit the size of your serving bowl for donburi, cut the unagi fillet in half or thirds.

Broil

• Place a rack about 8 inches (20 cm) away from the top heating element and turn the broiler* on high (550oF/288oC) for 5 minutes (in the center of the oven). * Low (450°F/232°C), Medium (500°F/260°C), and High (550°F/288°C) are the broiler settings. My preferred broil settings are High (8 inches away) or Medium (6 inches away). While broiling, you regulate the distance between the broiler and the food's surface rather than the oven's temperature. Using hotter and cooler zones on your barbecue is analogous.
• For simple cleanup, line a baking sheet with foil, then brush or spray the oil onto the foil. Put the skin-side down of the unagi pieces on the foil.
• There is no need to flip it; just roast it on one side.
• Brush the sauce over the unagi after turning the oven on. After that, broil the food once more for 30 to 60 seconds or until the sauce bubbles on top.