I made chicken katsu tonight following this recipe. I added peanut oil to the pan, let it get hot, then threw in my semi-frozen breaded chicken thighs. As you can see, I cooked them longer than called for because they hadn't totally dethawed yet. Suprisingly they came out very moist and delicious!
Anyway, I noticed a foam forming in the pan about midway through cooking. I took the picture below at the very end when I was taking out the chicken, and the foam was still there. What's the cause of this?