Combine the ground beef, ground pork, egg, minced onion, pressed garlic, herbs, salt, and pepper in large mixing bowl. Squeeze out the slice of bread, break it up, and add it to the bowl. Mix everything very well.
Preheat a large cooking pan that is also oven-safe over medium heat. Add a little oil for cooking meatballs.
Grease your hands with some cooking spray. Scoop out some meat using a cookie scoop and roll meatballs. (You can make meatballs bigger or smaller according to your own preference. Just remember to adjust cooking time if making bigger or smaller meatballs.)
Roll all the meatballs before adding them to the pan. Once all the meatballs are rolled, add them to the hot pan.
Cover with a lid and cook for a few minutes, then flip.
Pour marinara sauce over the meatballs and slowly stir.
Bake meatballs for about 20 minutes.
Add a little more minced basil over the top once the meatballs are done.