Prepare the Potatoes:
Mash the cooked potatoes in a large bowl, then mix in green onion, sour cream, salt, and pepper. Mash until mostly smooth, but leave a few chunks for texture.

Form the Balls:
Take a spoonful of the mashed potato mixture, flatten it in your palm, and place a cheese strip in the center. Wrap the potato mixture around the cheese to form a ball, ensuring the cheese is fully enclosed. Repeat with the remaining mixture.

Prepare the Coating:
Set up three bowls: one with flour, one with beaten egg, and one with a mixture of cornstarch and panko breadcrumbs.
Coat each potato ball in flour, dip into the beaten egg, and then roll in the panko breadcrumb mixture until evenly coated.

Fry the Potato Cheese Sticks:
Heat vegetable oil in a deep fryer or large pot to 350°F (180°C).
Fry the potato balls in batches for about 3 minutes, or until golden brown and crispy. Remove from oil and drain on paper towels.

Serve:
Serve hot and enjoy the crispy, gooey cheese-filled potato sticks!