Step 1

Arrange a rack in the middle of the oven and heat the oven to 350°F. Lightly coat a 9x13-inch or 3-quart baking dish with cooking spray. Prepare the following, placing them all in a large bowl as you complete them: Grate 1/2 medium yellow onion on the large holes of a box grater directly into the bowl to capture its juices (about 1 cup). Mince 3 garlic cloves, finely chop 1/4 cup fresh parsley leaves, and finely grate 2 ounces Parmesan cheese (about 1/2 cup).

Step 2

Add 1 1/2 pounds lean ground beef, 1/2 cup plain breadcrumbs, 1 large egg, 2 teaspoons Italian seasoning, 1 teaspoon kosher salt, and 1/2 teaspoon black pepper to the bowl. Gently mix with your hands until combined and no pockets of dry breadcrumbs remain.

Step 3

Grate 8 ounces mozzarella cheese on the large holes of the box grater (about 2 cups). Pour half of jar of marinara sauce (about 1 1/2 cups) into the bottom of the prepared baking dish and spread it into an even layer with a spoon.

Step 4

Form the mixture into 1 1/2-inch meatballs (about 2 heaping tablespoons each), wetting your hands with water as needed to prevent sticking, and arrange the meatballs in a single layer nestled in the sauce as they are made. (It’s OK if they are touching). You should have about 28 meatballs.

Step 5

Spoon the remaining sauce evenly over the tops of the meatballs and sprinkle the mozzarella cheese evenly over the top.

Step 6

Bake until the cheese is lightly browned, the sauce is bubbling around the edges, and the meatballs are cooked through (or an instant-read thermometer inserted into the center of a meatball registers at least 165°F), 35 to 40 minutes. Garnish with more parsley leaves, if desired.