Fill a 5 Qt pot with water. Add 1 tablespoon salt and peeled, quartered russet potatoes (2 lbs or about 7 medium potatoes). Cook until easily pierced with a fork. Drain well, mash with 4 tablespoons butter, and let cool to room temperature. Mashed potatoes can be made 1-3 days ahead.

In a large mixing bowl, combine 4 cups mashed potatoes, 2 cups shredded mozzarella cheese, 1 large egg, 1/4 cup flour, and 2 tablespoons chopped chives. Use a potato masher to mix everything until well combined. If the mixture is too loose to hold a patty shape, add more flour, one tablespoon at a time.

Take a heaping tablespoon of the potato mixture, place it between your palms, and form it into a round, 1/3-inch thick patty. Dredge both sides of the patty in bread crumbs and set it on a cutting board. Repeat with the remaining mixture.

Heat a large non-stick pan over medium heat with enough oil to lightly cover the bottom. Once the oil is hot, add the patties in a single layer and sauté for 3-4 minutes per side, or until golden brown. Repeat with the remaining patties, adding more oil as needed. Using two skillets can speed up the process.

Serve warm with a dollop of sour cream.