Peel and cube potatoes. Place into a large pot of water, ensuring it covers the top at least by 1″. On medium-high heat, bring to a boil and continue to boil until potatoes are soft and tender. Drain water and return potatoes to the pan. Mash with a potato masher. Let stand to cool for a bit.

Add cornstarch and shredded mozzarella to the cooled mashed potatoes. Season with salt and optional pepper. Mix well with a spoon, then knead by hand until a soft dough forms.

Divide the potato mixture in half. Place each half into a quart-size resealable bag. Press out the air and seal tightly. Flatten the dough evenly inside each bag using your hands.

While the dough chills, heat vegetable oil in a saucepan over medium heat. Oil should reach about 350°F for optimal frying. A deep fryer can also be used if available.

Remove the chilled dough from the bags and discard the plastic. Slice into ½-inch strips, then cut each strip in half for shorter sticks.

Working in batches, use tongs to gently lower each potato stick into the hot oil one at a time. Fry for 2–3 minutes, or until golden and crispy. Avoid overcrowding the pan.

Transfer fried sticks to a paper towel-lined plate to drain excess oil. Repeat until all are cooked.