Preheat oven to 400°F (200°C) and line a baking sheet with parchment paper or baking mat.

In a large mixing bowl, combine Italian breadcrumbs and milk. Stir well and let sit for at least 5 minutes while preparing other ingredients. This panade keeps meatballs extra tender and moist.

Add ground beef, diced onion, minced garlic, beaten egg, salt, black pepper, parmesan cheese, and parsley to the breadcrumb mixture. Mix with your hands until just combined - you should see no dry pockets of breadcrumbs, but mixture should still look slightly rough. Do not overmix as this creates tough meatballs.

Using a cookie scoop or ice cream scoop, portion the mixture onto the prepared baking sheet, leaving about 1 inch of space between each meatball. Wet your hands with water and gently roll each portion into a 2-inch diameter ball (approximately 1.5-2 oz each). The water prevents sticking and helps maintain tender texture.

Bake for 18-20 minutes, or until meatballs reach an internal temperature of 165°F (74°C). They should be golden brown on the outside. Remove from oven, carefully drain excess fat, and let rest for 3-5 minutes before serving with your favorite sauce.