Heat your wok on high, then when it’s hot, add oil (10 oz), enough so that it will completely submerge the fish when you add it later. Let the oil reach a temperature of 300° F (149° C).
When the oil has reached the correct temperature, it’s time to deep-fry the fish. Give each piece of fish a firm, gentle squeeze to help the cornstarch cling on, then lower the fish gently into the oil. Don’t drop it from a height! In fact, the best way to avoid splashing of hot oil is to have the bottom of the piece touching the oil, or very close to the oil, when you let go of the fish.
Wait 20-30 seconds before moving the fish around with your chopsticks or tongs. If you touch the fish immediately after it enters the oil, the cornstarch will come off. You want to wait for them to firm up a bit, then nudge them as necessary to prevent sticking.
You may need to divide your fish into two or more batches, as we do, to avoid overcrowding the wok. When you crowd too much fish into the wok, you risk the pieces sticking together, and the oil temperature also drops too much to deep-fry effectively.
Fry the fish until they turn a light yellow color, which should take about four minutes. Remove the fish from the wok with a spider strainer or slotted spatula. Set aside and repeat with the rest of the fish if you’re frying in batches.
Once all of the fish have gone through a first fry, proceed with a second round of frying.
Increase the heat to high, and bring the oil up to temperature of 400°F (205°C).
This second fry gives the fish the beautiful golden fried color and a crispy exterior. Again, you can divide the fish into two or more batches.
Add the fish back to the wok, and fry until they turn golden, which should take less than a minute. Our second fry only lasted 30-40 seconds.
Take the fish out. You can keep them in the spider strainer and set the spider on a plate to allow the excess oil to drain.
You can keep the frying oil to reuse later by letting it cool down, then pouring it into a container.