Instant Pot Recipe:

1. Turn Instant Pot to sauté setting. When display says HOT add in the oil and the onion. Sauté onion for 4-5 minutes. Then add in garlic and sauté for 30 seconds. 
2. Pour in the beef broth and scrape the bottom of the pot so that nothing is sticking. Turn off Instant Pot. 
3. Add in the meatballs. Pour the crushed tomatoes and tomato paste on top of meatballs. Sprinkle in the oregano. 
4. Cover Instant Pot and secure the lid. Make sure valve is set to sealing. Set the SOUP (or manual/pressure cook) button to 5 minutes. When time is up let pot sit for 5 minutes and then move the valve to venting. Remove the lid. 
5. Add a bit of the hot soup to the milk to temper it and then pour the milk into the pot. 
6. Turn off Instant Pot and move the inner liner to the countertop. Then add in the cheeses. This will prevent the cheese from sticking to the bottom of the pot.
7. Salt and pepper to taste. Ladle into bowls and top with additional parmesan cheese. Serve soup with buttered, toasted baguette slices, garlic bread or breadsticks. 

Slow Cooker Recipe:

1. Heat pan over medium high heat and add in the oil and the onion. Sauté onion for 4-5 minutes. Then add in garlic and sauté for 30 seconds. Transfer contents to the slow cooker. 
2. Pour in the beef broth, meatballs, crushed tomatoes, tomato paste and oregano. 
3. Cover and cook on low for 4-6 hours.
4. Add a bit of the hot soup to the milk to temper it and then pour the milk into the slow cooker. 
5. Stir in the cheeses. Salt and pepper to taste. Ladle into bowls and top with additional parmesan cheese. Serve soup with buttered, toasted baguette slices, garlic bread or breadsticks.