How to Make It
Preheat oven to 450°F. Lightly coat 2 rimmed baking sheets with cooking spray; arrange wings on one baking sheet.
Cut leek in half lengthwise; rinse well and pat dry. Separate whites and greens; set aside greens. Arrange leek whites, celery, onions, carrots, and garlic on second baking sheet.
Roast wings and vegetables until lightly golden, about 30 minutes for vegetables and 1 hour for wings.
Transfer roasted wings and vegetables to a large stockpot; add lemon peel, bay leaves, peppercorns, reserved leek greens and 6 quarts cold water. Bring to a boil over medium. Reduce to a simmer; cook, skimming foam often, until stock is flavorful, 3 to 4 hours.
Pour stock through a fine-mesh sieve into a large bowl; discard solids. Serve warm, or let cool 30 minutes to 1 hour before transferring to airtight containers. Stock keeps refrigerated for 1 week or frozen for up to 6 months.