One by one, dip in the beaten egg, coating completely, and then roll in bread crumbs to coat.
Put the sticks on a plate and freeze for 15 minutes.
Heat a deep fryer or heavy pot to 365 in 3 inches of oil.
Fry the mozzarella sticks in 2 batches until golden brown, about 1 minute.
Drain on paper towels and serve with hot marinara sauce.