Preheat oven to 400°F. Line a baking tray with parchment paper and set aside.
In a medium bowl, combine milk, breadcrumbs, parsley, egg, and onion soup mix. Mix until well combined.
Add beef, parmesan if using, salt, and pepper, and combine until just mixed through, being careful not to overmix.
Using a 1½ Tablespoon cookie scoop (or a spoon), make 24 meatballs. Gently roll in your palms to create round balls. Lay the meatballs about an inch apart on baking tray.
Bake meatballs for 12-15 minutes, or until meatballs reach an internal temperature of 160°F.
Notes
* You can substitute the French Onion Soup Mix with:
1 Tablespoon onion flakes
1 Tablespoon onion powder
½ teaspoon garlic powder
⅛ teaspoon paprika
Leftover meatballs can be stored in an airtight container in the fridge for up to 4 days.