Heat olive oil in a small skillet over medium heat. Add onions and cook for 5 minutes. Add garlic and cook for 1 more minute. Set aside and let cool.
Combine the breadcrumbs, Parmesan cheese, oregano, salt, and pepper and set aside.
Crack an egg in a small bowl and whisk it. Add the milk and whisk to combine.
Combine the dry mixture with the wet mixture to form a smooth paste. Mix in the onions and garlic. (This is called a panade and keeps the juiciness and flavor intact while the meatballs cook.)
Add the meat to a large bowl and top with the panade. Use your hands and gently mix until just combined. Don’t overwork the meat or the meatballs will be tough.
Roll into 1 ½ inch meatballs.
Pour ¾ of the marinara sauce on the bottom of a 9×13 inch casserole dish. Add the meatballs. Spoon remaining sauce over the top.
Cover and bake for 30 minutes.
Uncover and top with cheese. Bake 15 more minutes. Broil for additional 1-2 minutes at the end if desired. Sprinkle with parsley and serve.
Notes
To save time, you can skip sautéing the onions and garlic. Doing so creates a more subtle texture and flavor, particularly for picky eaters.
Ground sausage and/or ground veal may also be used.
The internal temperature of meatballs should be 160 degrees before serving.
Make Ahead Method
These meatballs can be rolled and stored in the refrigerator for up to 24 hours prior to baking.
You can also flash freeze the raw meatballs on a baking sheet for 1.5 hours, then store them in a gallon freezer bag for up to 3 months. Let them defrost in the fridge overnight prior to baking.
Crock Pot Method
Roll the meatballs and place them in a lightly greased Slow Cooker. Top with marinara sauce and heat on high for 3-4 hours or on low for 6-7.
Storage
Store in an airtight container and refrigerate for up to 3 days or freeze for up to 3 months.
