Boil and mash the russet potatoes in salted water until fork-tender, then drain and mash with unsalted butter and milk, seasoning with salt and pepper.

Chill the mashed potatoes in the refrigerator for 30-60 minutes.

Prepare the beef filling by browning the lean ground beef and adding onion and garlic; stir in smoked paprika and oregano, then allow to cool.

Shape potato balls by flattening mashed potatoes, adding beef filling and cheddar cheese, then rolling into a ball.

Set up a breading station with flour, egg mixture, and Panko breadcrumbs; coat each potato ball in this order.

Fry the potato balls in heated vegetable oil until golden brown and crispy, about 4-6 minutes.

Serve the fried potato balls garnished with fresh parsley.