Note: this batch made 18 meatballs but I only cooked off half of them, storing the other half in the fridge. So the ingredients amounts listed for the tomato sauce are enough for 9-10 meatballs. If you're cooking off the entire batch of meatballs simply double the ingredient amounts for the tomato sauce.
Start by roasting 3 tomatoes in the oven at 400F. (Normally they need about 20-30 minutes to fully roast, but I usually take them out when I need them because there is an extended simmer coming up.)
Saute a roughly chopped onion and 3 whole, peeled garlic cloves in a dollop of oil over medium heat. Cook until the onion is starting to brown.
Add the onion, garlic, and roasted tomatoes to a blender. Combine well. If you want a spicy version you can optionally add 3 chipotles in adobo. (I usually scrape out the seeds of the chipotles.)
You'll need 1/2 cup chopped mint for the meatballs. Pull the leaves off of 8-10 mint sprigs. Rinse and finely chop them.
Add the mint to a large mixing bowl along with 1 lb. ground beef, 1/2 lb. ground pork, 2 eggs, 1/4 onion (finely chopped), 3 minced garlic cloves, 2 teaspoons salt, freshly cracked black pepper, and 1/2 cup of cooked white rice.
Combine well and then use your hands to form meatballs that are approximately 1 inch wide. Keeping your hands wet will help if the mixture is sticky.
I usually brown the meatballs first but this is an optional step. You can always add them directly to the tomato sauce knowing they will need a longer simmer. To brown them, heat up a thin layer of oil in a skillet over medium heat. Add the meatballs and turn them regularly to give them a char on all sides. This batch was in the pan for 4-5 minutes.
To finish the tomato sauce, heat up a dollop of oil in a saucepan over medium heat. Add the blended tomato mixture and simmer for a few minutes until it reduces down a bit. Add 1-2 cups of stock, 1/2 teaspoon of salt, and 1/2 teaspoon Mexican oregano (optional). Simmer for a few minutes until everything is at a uniform temperature.
Add the meatballs to the tomato mixture and simmer, covered, until the internal temperature of the meatballs is approx. 160F. That took 15 minutes for this batch. It will take approx. 30-40 minutes if you skip the browning step.
Take a final taste for seasoning as these meatballs are hyper-sensitive to salt amount, adding more salt if necessary.
Serve immediately with plenty of the tomato sauce covering them.