Cut chicken to tiny bite sized pieces. Make sure you cut them to uniform sizes as this helps to cook uniformly.
In a bowl, mix together seasoning and chicken well. Optionally add 2 tbsps buttermilk or yogurt and mix well. You can refrigerate this for 30 mins to 8 hours.
Pour the egg white or buttermilk and mix well. Sprinkle cornstarch in 2 batches and coat the chicken well. At this stage your chicken must have a thick and moist batter coated over it and should not be dry.
Add panko crumbs to a plate or bowl. Place the bowl of chicken and the plate of panko crumbs, side by side.
Pick up each piece of chicken & roll in the bread crumbs. Press down gently each piece with your fingers to coat the chicken with the crumbs. This gives results similar to double breading.
Place them in a wide tray. Repeat the same step until all the chicken bites are breaded.
Rest for 10 to 15 mins for the bread crumbs to stick well to the chicken. You can also refrigerate in a air tight container up to 48 hours for further use.
Pour oil to a deep pan and heat on a medium flame until hot enough.
Oil has to be medium hot and not smoking hot. Test by dropping a small piece of bread crumb into the oil, it should sizzle and come up to the surface without become brown or burnt. This means the oil is at the right temperature for frying. If the crumb sinks, it means the oil is still not hot enough.
350 to 375 F is the right temperature if you are measuring.
Gently drop the breaded popcorn chicken to the hot oil one after the other. Do not stir or disturb them for about a minute or 2, as this is going to separate the bread crumbs from the chicken.
Do not crowd the pan with many chicken bites at one time as this will bring down the temperature of the oil. Fry popcorn chicken in batches.
Stir after 2 mins and fry evenly till golden and crisp on a medium flame. The internal temperature of the thickest piece of fried chicken should reach 165 F. If you don't have a food thermometer, simply cut down a popcorn chicken. It should not be pink inside any more.
Remove the popcorn chicken to a cooling rack placed over kitchen tissues or a tray. Or to a steel colander.
To fry the next batch of popcorn chicken, turn down the heat to low. Using a mesh skimmer, remove any bread crumbs that have fallen off to the oil. Bring the oil back to right temperature and fry them in batches.
Place the tray in a 375 F or 190 C, preheated oven in the middle rack. Bake for 14 mins or until the chicken is cooked through, turning them half way.
Place the breaded chicken in the air fryer basket and air fry for 10 mins at 400 F or 200 C. Turn them after 5 mins. Adjust the cook time as required as this significantly changes with marinade timings and the size of your pieces.
The internal temperature should reach 165 F or 74 C. Once done, cut down a piece of chicken to see if it is done. The inside should no more be pink in color.
You can sprinkle your favorite seasoning over popcorn chicken before serving. Sriracha or wasabi go great on these.