Mix together the ground beef, onion, celery leaves, bread crumbs, eggs, salt and pepper. Shape into one inch meat balls. Set aside and prepare the vegetables.
Put the 2 tablespoons of olive oil in a dutch oven or large pot. Peel and wash the potatoes, carrots, celery and onions. Cut the potatoes and onion in half. Cut the carrots and celery into 1 inch pieces. Add to the pot with the olive oil. Add 1 cup of water and the 3 cups of beef broth and bring to a boil. Reduce heat to a simmer and add the meatballs. Salt and pepper to taste. Cover and cook for 30 minutes.
To thicken the broth (optional), add the 2 tablespoons of flour to the broth or water and mix well. Add to the stew slowly. Cook for another 3-4 minutes until thickness you desire is reached
If desired, add two cups chopped tomatoes with carrots and celery. to stew.