quanjude + teriyaki sauce

Earlier last month, my family and I dined at Melbourne's Quanjude (the main branch is in China) for dinner. Actually the main purpose was to try their Peking duck, since they are famously known as "the duck specialist".
It was a tasty experience despite staff calling us at 10 PM confirming the reservations. I've also eaten this dish in Malaysia and Taiwan. From my experience in Malaysia they only slice the crispy skin for the wrapping. The other part of the duck is usually deboned and mixed with stir fry noodles and chopped up. Same with the roast pig, only the crispy skin is served.

The chef thinly slicing a freshly roasted Peking duck

We also tried some prawn, wagyu, hot pot dishes as well and one of the dishes that caught my uncle and dad's eye was the thinly sliced wagyu wrapped around enoki mushrooms which were priced at around $4~$5 per roll. Dad remade this ate home with scotch fillet (seen above) whilst my uncle and I had a teriyaki sauce cook off.
Apparently my sauce was better because it was sweeter which matched the flavour at the restaurant, but Uncle's sauce was good too. I reckon they tasted pretty similar except Uncle's sauce had a dash of chili powder added to it. I don't know his secret recipe but I'll post my not so secret recipe :P
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teriyaki sauce
ingredients:

• 100 ml mirin
• 100 ml cooking sake
• 100 ml soy sauce (Kikkoman)
• 25 grams sugar

method:

1. Place all ingredients into a small saucepan and bring to a boil stirring so the sugar dissolves. Lower the heat to simmer and let it reduce by a quarter.
2. To thicken, dissolve 1 tsp of potato starch into 2 tsp of water and add it to the boiling liquid.
   Stir until thickens.

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Note: Uncle said it will taste better if I add a tad more sake to it. Will do more experimenting on it. But for now, this sauce is good enough for me to eat it with plain rice :D