In a large bowl, combine the beef, Italian sausage, eggs, onion, garlic, bread crumbs, cheese, and 1 teaspoon of salt and pepper (each). Mix until fully combined.
Moisten hands and shape medium-small meatballs. Place them on a platter.
In a large frying skillet over medium heat, warm the oil.
Working in batches, add the meatballs to the hot oil and brown on all sides, about 6 - 8 minutes. The insides won't be completely cooked at this point.
Finish Off the Soup
Using a slotted spoon, carefully add the meatballs to the soup and simmer gently over low heat until they are cooked through, about 20 minutes.
Taste, and add salt accordingly, usually anywhere from 1 tablespoon to 2 tablespoons, depending on if the broth was seasoned or not. Taste and then add in increments, continuing to taste until just right.
Ladle soup into warmed soup bowl and top with grated cheese.