Step 1

Arrange a rack in the middle of the oven and heat the oven to 400°F. Line a rimmed baking sheet with parchment paper.

Step 2

Dice 1 small yellow onion (about 2/3 cup). Mince 4 garlic cloves and place half in a large bowl. Finely chop the leaves and tender stems of 1 small bunch fresh parsley until you have 1/4 loosely packed cup and add it to the bowl (chop more for garnish if desired). Finely grate 1 ounce Parmesan cheese (about 1/2 packed cup) or measure out 1/3 cup store-bought grated, and add half to the bowl.

Step 3

Add 8 ounces ground beef, 8 ounces ground pork, 2/3 cup panko or fresh breadcrumbs, 1/4 cup milk, 1 large egg, 1 teaspoon of the kosher salt, and 1/4 teaspoon black pepper to the bowl. Mix lightly with a fork until just combined.

Step 4

Form the mixture into 16 to 18 (about 1 1/2-inch) meatballs (about 2 tablespoons each), wetting your hands with water as needed to keep the mixture from sticking. Place on the baking sheet, spacing them evenly apart.

Step 5

Bake until browned and cooked through or and an instant-read thermometer inserted into the center of a meatball registers at least 165°F, 15 to 20 minutes.

Step 6

Meanwhile, bring a large pot of heavily salted water to a boil over high heat. Start the sauce: Heat 2 tablespoons olive oil in a large pot or Dutch oven over medium heat until shimmering. Add the onion and sauté until softened and translucent, about 5 minutes. Add the remaining garlic and 1/4 teaspoon red pepper flakes, if using. Sauté until fragrant, about 1 minute.

Step 7

Carefully add 1 (28-ounce) can crushed tomatoes and the remaining 1/2 teaspoon kosher salt, and stir to combine. Cover and bring to a simmer over medium-high heat. Reduce the heat to low. Cover with the lid ajar and continue to simmer gently, stirring occasionally, until the meatballs are ready.

Step 8

Using tongs or a slotted spoon, transfer the meatballs to the sauce. Gently stir to coat the meatballs and submerge them in sauce. Continue to simmer gently, covered with the lid ajar, while you cook the pasta.

Step 9

Add 1 pound dried spaghetti to the boiling water and cook according to package instructions until al dente, about 10 minutes. Reserve 1/2 cup of the pasta water, then drain the pasta. Return the pasta to the now-empty pot off the heat. Add a few ladlefuls of sauce from the pot of meatballs and toss to coat, adding the reserved pasta water a tablespoon at a time as needed to loosen the sauce and coat the pasta.

Step 10

Transfer the pasta to individual shallow bowls or plates and top with the meatballs and more sauce. Serve garnished with the remaining Parmesan cheese and chopped parsley.