Step 1: In a large bowl, combine ground beef, ground pork (if using), uncooked white rice, 1/4 cup chopped fresh mint, 1/4 cup chopped fresh cilantro, 1/2 small finely diced onion, 2 minced garlic cloves, the lightly beaten egg, 1 teaspoon salt, and 1/2 teaspoon black pepper. Mix gently with your hands until just combined, being careful not to overmix.
Step 2: Form the meat mixture into small meatballs, about 1.5 inches in diameter. You should get approximately 25-30 meatballs. Set aside.
Step 3: Heat olive oil in a large Dutch oven or heavy-bottomed pot over medium heat. Add the remaining diced yellow onion and 4 minced garlic cloves, sautéing until softened and fragrant, about 3-4 minutes.
Step 4: Add the diced carrots and celery to the pot, cooking for another 5 minutes, stirring occasionally, until they begin to soften.
Step 5: Stir in the canned diced tomatoes (with their juice) and tomato paste. Cook for 2-3 minutes, stirring to deepen the tomato flavor.
Step 6: Pour in the beef broth and chicken broth. Add the bay leaf, ground cumin, dried oregano, and optional red pepper flakes. Bring the broth to a gentle simmer.
Step 7: Carefully drop the prepared meatballs into the simmering broth. Do not stir vigorously. Let the meatballs cook gently for about 10-15 minutes until they are mostly firm.
Step 8: Add the diced potatoes to the soup. Continue to simmer for another 10-12 minutes, or until the potatoes are almost tender.
Step 9: Stir in the diced zucchini. Cook for an additional 5-7 minutes, or until all the vegetables are tender but still hold their shape. The meatballs should be fully cooked through at this point.
Step 10: Remove and discard the bay leaf. Taste the soup and adjust seasonings with salt and pepper as needed. Stir in additional fresh cilantro or mint if desired for a final burst of freshness.
Step 11: Ladle the hearty albondigas soup into bowls. Serve hot with fresh lime wedges on the side for squeezing over each serving. Enjoy this delicious albondigas soup recipe!