Drain the shucked oysters from the plastic container, and give them a gentle rinse with cold water. The oysters are very delicate, so be careful handling them. Place the oysters in a colander, and let the excess water drain for at least 10 minutes.
Prepare the batter by mixing ¾ cup flour, the baking powder, white pepper, garlic powder, onion powder, and salt until well-combined.
Heat the oil to 350 degrees F in a small (to save oil) but deep pot (to prevent splattering). Check the oil temperature with a candy or oil thermometer for accuracy.
Right before you’re ready to fry the oysters, add the cold seltzer––it makes for a crispier oyster. Mix until your batter is smooth (a few small lumps here and there is fine). Then, mix in the sesame oil.
After the oysters have drained, lightly pat each of them dry with a paper towel, and dredge each oyster lightly with flour. I know it’s tempting to dredge all of the oysters at once in a glob, but it’s best to dredge each oyster individually just before you batter and fry them to ensure they are fully and evenly coated.
After dredging, dip each oyster into the batter so it is fully coated. Lift them out of the batter carefully--you can use the edge of the bowl to scrape off excess batter if needed.
Now you’re ready to deep fry the oysters. Check the temperature of the oil again with your thermometer. As you are frying, you should adjust the heat to maintain a temperature between 325 degrees F and 350 degrees F, because the oil will cool quickly as you drop in the battered oysters and then quickly heat again as they cook.
Lower the oyster halfway into the oil and slowly swirl it for 2 or 3 seconds so the batter cooks slightly, and then drop it into the oil. This process prevents the oyster from sticking to the bottom of the pot. Fry the oysters in batches, depending upon the size of your pot and the amount of oil you are using. For this recipe, we fried oysters in batches of 3 or 4 depending upon their size.
Use a slotted spoon to lift the oysters out when they are golden brown and transfer them to a metal cooling rack to drain. Repeat until all the oysters have been fried.
Now you can make the dipping sauce. In a small saucepan, add the ketchup, soy sauce, rice vinegar, salt, sugar, and cornstarch slurry and heat to a simmer. You can adjust the flavor by either adding vinegar to make it more tart, adding sugar if you like it sweeter, or adding more cornstarch and water if you like it thicker.
It’s best to serve these immediately, but if you are like us on Chinese New Year, you are preparing many dishes at the same time, and it’s inevitable that these won’t get eaten immediately! So just before serving, you can reheat your oil to 375 degrees F, and drop the oysters in 3 or 4 at a time, frying them for 30 seconds or until they are crisp again. Alternatively, you can heat them in a toaster oven at 400 degrees F for 5 minutes.
Serve these deep fried oysters on a bed of iceberg lettuce, and garnish with chopped scallions. The dipping sauce should be served warm, so reheat your dipping sauce if needed.