Prepare the Meatball Mixture: In a large bowl, combine the lean ground beef, plain breadcrumbs, large egg, finely chopped onion, minced garlic, salt, and pepper. Mix gently to combine, then refrigerate for about 30 minutes.

Form the Meatballs: Preheat your oven to 400°F (200°C). Shape the meat mixture into 1-inch meatballs and place on a lined baking sheet. Bake for 15-20 minutes until golden brown.

Sauté the Vegetables: In a large pot, heat olive oil over medium heat, add diced carrots and celery, and sauté for 5 minutes.

Simmer the Broth: Pour in the broth and diced tomatoes, bring to a gentle boil, and let it bubble for 2-3 minutes.

Add the Meatballs and Cook: Reduce heat to low and add baked meatballs. Simmer uncovered for 20 minutes, stirring occasionally.

Final Touches and Serve: Taste and adjust seasoning if needed, add pasta or rice if using, cook until tender, and serve hot with herbs.