1. Preheat the oven to 375ºF.

2. In a large pan, heat the olive oil over medium-high heat. Add the onion and sauté, stirring frequently, until translucent but not beginning to brown, about 2 minutes. Add the garlic and sauté, stirring, until fragrant but not beginning to brown, about 1 minute more. Transfer the sautéed aromatics to a plate (spread them out on the plate for faster cooling) and set aside to cool.

3. Tear the buns or bread slices into small pieces, then place in a small bowl. Pour over the milk. Using your hands, toss together the bread and milk to saturate, then set aside to soak for about 2 minutes.

4. In a large bowl, combine the ground beef, parsley, eggs, Parmesan, and seasoned breadcrumbs. Add the cooled aromatics (they should not be hot!) to the bowl, along with the soaked bread and any milk left in the small bowl (the milk will help tenderize the meat, while the bread will make the meatballs more moist). Add a pinch of salt and freshly cracked black pepper to taste.

5. Using your hands, mix and fold everything to just combine, being careful not to over-mix. Evenly coat 1–2 rimmed baking sheets with a thin layer of olive oil.

6. Scoop 16–20 equal-sized balls of the meat mixture onto the prepared baking sheets, spacing them apart (I use an ice cream scoop for this, but you can also use a spoon, measuring cup, or your hands). Using your hands, gently roll the meat mixture into about 2-inch balls. Spray the meatballs lightly with cooking spray.

7. Transfer the meatballs to the oven and roast until browned on top and cooked through, about 20 minutes. Let the meatballs rest for about 5 minutes, then serve!