Steps

1. In a bowl, mix 1 tbsp mayonnaise, 1 tsp cooking sake, and 1 pinch salt until well combined. *Key tip!* The oil from the mayonnaise coats the chicken and the sake enhances moisture retention, resulting in incredibly juicy chicken. *Key tip!* It's okay if it looks lumpy right after mixing; it will come together with time.
   🕒 01:05
2. In a separate bowl, combine 1.5 tbsp soy sauce, 2 tbsp mirin, 1 tsp sugar, and 1 tsp vegetable oil. Mix thoroughly until the sugar dissolves. *Key tip!* Adding oil prevents the sauce from burning and makes cooking significantly easier.
   🕒 02:13
3. Prepare a shallow dish or plate with 4 tbsp potato starch. *Key tip!* Having a little extra ready makes the next step smoother and helps the starch adhere better.
   🕒 03:14
4. Trim only the protruding white sinew from the chicken tenderloins with scissors. *Key tip!* Removing only the visible white sinew simplifies preparation without affecting the texture.
   🕒 04:03
5. Lay the chicken tenderloins on a cutting board, cover with plastic wrap, and gently pound with the palm of your hand. Avoid pressing too hard. *Key tip!* Finely pounding breaks down the chicken's fibers, making it incredibly tender and melt-in-your-mouth. The goal is not to flatten it.
   🕒 06:26
6. Thinly spread the prepared mayonnaise mixture evenly over both sides of the pounded chicken tenderloins. *Key tip!* Applying a thin layer creates an oil barrier from the mayonnaise, maintaining juiciness.
   🕒 07:55
7. Cut 3 slices of cheese in half and place one half on each chicken tenderloin.
   🕒 09:36
8. While holding the cheese in place, fold each chicken tenderloin in half. Coat both sides thoroughly with the prepared potato starch. Lightly tap to shape, ensuring the edges stick together, and dust off excess starch. Reinforce with more potato starch if any parts seem to be peeling off. *Key tip!* Insufficient potato starch will clump due to the chicken's moisture, so be generous. *Key tip!* The potato starch helps the sauce adhere better and acts as a barrier to retain the juiciness from the mayonnaise coating.
   🕒 10:44
9. Place the shaped chicken tenderloins in a non-stick skillet with the folded edge facing down. *Key tip!* Since potato starch is less prone to burning, you can cook without oil.
   🕒 11:39
10. Heat the skillet over low heat. Once you hear the chicken sizzling, cover with a lid and cook for 5 minutes. *Key tip!* Cooking slowly over low heat ensures thick chicken tenderloins remain juicy. *Key tip!* If the mayonnaise is applied thinly, its acidity and flavor will barely be noticeable after cooking.
    🕒 14:52
11. Remove the lid, flip the chicken tenderloins, cover again, and cook for 4 minutes.
    🕒 16:03
12. Turn off the heat temporarily. Pour the prepared teriyaki sauce around the edges of the pan. *Key tip!* Turning off the heat before adding the sauce prevents it from boiling down too quickly, allowing you to work calmly.
    🕒 16:54
13. Once it lightly simmers, gently shake the pan to distribute the sauce. Flip all the pieces to coat them with the sauce. Turn the heat back on (very low to low) and simmer, coating the chicken with the sauce as it thickens. *Key tip!* Because there is oil in the sauce, it is less likely to burn even when reduced.
    🕒 17:21
14. Arrange the cooked chicken tenderloins on a plate and drizzle with any remaining sauce. Garnish with toasted sesame seeds and a sprinkle of shichimi togarashi, if desired.
    🕒 18:43