Italian Meatballs, Easy

2 ½ ounces (75g) fresh, crustless white bread, diced (about 2 unpacked cups)
½ cup (120ml) whole milk
1 small (6-ounce) yellow onion, finely diced, or 1 teaspoon onion powder
6 medium cloves garlic, minced, or ½ teaspoon granulated garlic
1 ½ ounces (45g) finely grated Parmigiano-Reggiano, plus more for serving
3 large egg yolks
⅓ cup loosely packed flat-leaf parsley leaves and tender stems (¾ ounce; 20g), minced
2 teaspoons (8g) Diamond Crystal kosher salt; for table salt, use half as much by volume or the same weight
½ teaspoon freshly ground black pepper
1 teaspoon dried oregano
¾ teaspoon ground fennel seed
1 ½ pounds (680g) ground meat (either all pork, 1 pound pork and ½ pound beef, or ½ pound each pork, beef, and veal; see notes)
1 recipe Quick and Easy Italian-American Tomato Sauce (or your preferred sauce), warmed through

Preheat broiler and set oven rack about 4 inches from broiler element; line a rimmed baking sheet with parchment or foil. In a large mixing bowl, combine bread with milk, tossing to coat. Let stand, tossing occasionally, until bread is completely moist, about 10 minutes. Squeeze bread between your fingers or mash with a spoon to make sure there are no dry spots.
Add onion, garlic, Parmigiano-Reggiano, egg yolks, parsley, salt, pepper, oregano, and fennel to bread mixture and, using a clean hand or spoon, stir until very thoroughly incorporated. Add ground meat and, using your hand, continue mixing vigorously, squishing meat and seasonings between your fingers, until very thoroughly combined and meat has taken on a slightly sticky texture.
Using your hands, roll meatballs to your desired size and arrange, evenly spaced, on prepared baking sheet.
Transfer to broiler and cook until browned on top, about 10 minutes (broiling time will vary greatly depending on the strength of your broiler, so keep a close eye). Using tongs, rotate meatballs and broil until well browned on second side.
In a large sauté pan or pot, combine meatballs and any accumulated juices with tomato sauce and bring to a simmer over medium heat. Cook, spooning sauce over meatballs and rotating meatballs occasionally, until meatballs are fully cooked through and register about 145°F (63°C) on an instant-read thermometer, 5 to 10 minutes. Serve, sprinkling additional grated cheese on each plate.

Try to get fattier ground meat, if possible; around 25% fat is a good rough percentage. This amount of fat will make for juicier and more flavorful meatballs than lean ground meat will