Combine the beef with the eggs, bread crumbs, cheese, and good-size pinches of salt and pepper in a mixing bowl. Being careful not to overwork the mixture, lightly form it into meatballs roughly 3⁄4-inch in diameter, a bit smaller than a golf ball. Heat the olive oil in a large pot over medium-high heat. Add the onion, carrots, and celery and sauté until the vegetables have softened, about 5 minutes. Add the stock and the escarole and bring the soup to a simmer. Turn the heat down to low and add the meatballs and pasta. Simmer for another 8 to 10 minutes, until the meatballs are cooked through and the pasta is al dente. Taste and adjust the seasoning with salt and pepper. Serve the soup with extra cheese on top.