In a small bowl, combine the egg, celery leaves and cheese. Crumble beef over mixture and mix well. Shape into 1-1/2-in. balls. In a large skillet, brown meatballs in oil in batches; drain.
In a small saucepan, combine the tomatoes, tomato paste, bread, garlic, sugar, pepper and salt; add meatballs. Bring to a boil. Reduce heat; cover and simmer for 30 minutes or until meatballs are no longer pink and sauce is slightly thickened, stirring occasionally. Serve with vermicelli; sprinkle with additional cheese.