In an 8-quart pot or Dutch oven, brown the ground beef and pork over medium-high heat until no pink remains. Drain. Set aside.
In the same pot, add the onion and cook until softened, stirring often. (There should be some grease left in the pot from the beef, but at this point, you can add a teaspoon or two of oil to the pan to cook the onions.) Add the garlic and taco seasoning and stir for one minute, allowing the spices to become very fragrant.
Begin adding the tomatoes, crushing them by hand as you add them. Add any remaining liquid in the cans to the pot.
Add the drained beef, beans, green chilies, and corn, if using. Stir well.
Begin adding the beef stock, stirring and adding more stock until the desired consistency. Some people prefer a thick, hearty soup while others would like more broth.
Taste for seasoning and adjust as desired. (The DIY Taco Seasoning does not contain salt, so most likely you will need to add more salt, depending also on the salt content of the stock, beans, etc.) Feel free to add more of the taco seasoning also.
Bring the soup up to a gentle simmer. Simmer for approximately 15 to 20 minutes (or longer), stirring often, to allow the flavors to marry.
Serve the soup with any desired toppings.