In a large bowl, mix the ground beef and pork together. Add the egg, uncooked rice, and yerba buena (mint); mixing it well. Make balls out of the meat mixture that are approximately 1 to 2 inches in diameter; set these to the side while you prepare the broth. This should make about 2 dozen (24) meatballs.
In a large soup pot or Cast iron Dutch oven, heat the vegetable oil over medium heat.
Add the onion and saute until clear. Add the garlic and continue to saute for another minute. Add the beef broth and the canned tomatoes to the soup pot and increase the heat so it comes to a full boil.
Carefully add the prepared meatballs, 1 or 2 at a time, to the boiling mixture. NOTE: You want to add them slowly enough that the broth is still boiling when you add more (this helps to keep the meatballs together by quickly cooking the outside of the meatball).
Once all the meatballs are added, reduce the heat to medium low and cover. Continue to cook for 30 minutes, without stirring. Remove from heat.
Makes about 6 servings.
Meatball Soup Recipe - Sopa de Albondigas: https://whatscookingamerica.net/cynthiapineda/sopa/sopa.htm