Beat milk and egg together in a large bowl. Mix bread crumbs in until a paste forms. Add ground beef, onion, garlic, and parsley, and mix with your hands until just combined.

Preheat the oven to 350 degrees F (175 degrees C). Coat a baking sheet with cooking spray.

Measure meatballs using an ice cream scoop. Roll balls with dampened hands and place on the prepared baking sheet

Bake in the preheated oven until meatballs are no longer pink in the center and an instant-read thermometer inserted into the center should read at least 160 degrees F (70 degrees C), about 30 minutes.

While meatballs bake, heat tomato sauce in saucepan over medium heat.

Add baked meatballs to the sauce and simmer, uncovered, for 30 minutes.