Step 1: Preheat your oven to 400°F (200°C).
Step 2: In a skillet, heat the olive oil over medium heat. Add the finely chopped leeks and sauté for about 3-4 minutes until soft and translucent.
Step 3: In a large mixing bowl, combine the cooked leeks, 1/2 cup of grated parmesan cheese, plain bread crumbs, kosher salt, milk, Worcestershire sauce, and eggs. Mix well until evenly incorporated.
Step 4: Gently fold in the lean ground beef into the mixture, being careful not to overmix.
Step 5: Form the mixture into meatballs about 1.5 inches in diameter and place them on a baking sheet lined with parchment paper.
Step 6: Bake the meatballs for 20-25 minutes or until browned and cooked through.
Step 7: Remove from the oven and serve with your favorite pasta, in a sandwich, or on their own with a sprinkle of remaining parmesan cheese.