Easy Spaghetti and Meatballs

Name: Easy Spaghetti and Meatballs
Ingredients: ¼ cup extra-virgin olive oil, plus more; 5 garlic cloves, sliced; 4 tsp. Diamond Crystal or 2½ tsp. Morton kosher salt, divided, plus more; 2 24.5-oz. bottles tomato passata; 1 cup whole milk; ½ cup seasoned Italian breadcrumbs; 1 large egg; ⅓ cup finely grated Parmesan, plus more for serving; ¼ cup finely chopped parsley, plus more for serving; 2 tsp. soy sauce; ¼ tsp. freshly ground pepper, plus more; ½ medium onion; 1 lb. ground beef, preferably 20% fat; 8 oz. ground pork; 1 lb. spaghetti