Start by peeling and cutting russet potatoes into 1-inch cubes. Place in a large pot with garlic and salt, cover with cold water, and bring to a boil. Simmer for about 15 minutes until tender, then drain.

In a large mixing bowl, combine drained potatoes with cream cheese, butter, and black pepper. Mash together until well combined but still slightly chunky.

Prepare an egg wash by whisking eggs and flour in a shallow dish, seasoned lightly with salt. In another dish, spread out breadcrumbs.

Take about ½ cup of potato mixture, flatten it, place a small cube of mozzarella in the center, fold the edges over, roll into a ball, and coat in the egg wash followed by breadcrumbs.

Heat about 1 inch of oil in a deep frying pan to 350°F. Fry croquettes for 2-3 minutes per side until golden-brown. Transfer to a paper towel-lined plate.

Serve immediately with marinara sauce for dipping or a fresh salad.