Preheat the oven to 375°F (190°C).
Arrange the turkey wings, celery, onion, and garlic in a 6- to 7-quart Dutch oven. Roast uncovered on the lower oven rack for approximately 2 hours, until the wings and vegetables are well browned. Do not add oil or water during roasting. If they begin browning too quickly, loosely cover the Dutch oven with foil to prevent burning.
2 turkey wings, 4 ribs of celery, 1 large yellow onion, 4 cloves garlic
Add 6 cups (1.4 L) water to the roasted turkey wings and vegetables. Place the Dutch oven on the stovetop and bring to a boil. Reduce to a simmer and cook uncovered for 1 hour to develop and concentrate the turkey stock.
6 cups (1.4 L) water
Strain the stock through a fine-mesh sieve into a heatproof container, discarding the solids. Refrigerate for at least 2 hours or overnight, until the fat has collected on the surface and can be removed. Skim off the fat and measure 2 cups (480 ml) of stock for the gravy. If there's a little extra, save it for thinning the gravy when reheating.
Melt the butter in a large sauté pan over medium heat. Whisk in the flour and cook for approximately 2 minutes, stirring constantly. The mixture should be smooth and bubbling as the flour cooks, but there's no need to brown it.
4 tbsp (56 g) salted butter, ¼ cup (30 g) all-purpose flour
Slowly whisk 2 cups (480 ml) of the defatted turkey stock into the roux, adding a small amount at first and whisking until smooth before adding more. Continue cooking over medium heat, stirring frequently, until the gravy thickens enough to coat the back of a spoon.
2 cups (480 ml) homemade turkey stock
Stir in the whole milk and continue cooking until the gravy is smooth and heated through. Remove from the heat, stir in the apple cider vinegar, and season with salt and black pepper to taste. Serve immediately, or cool and refrigerate for Thanksgiving Day.
½ cup (120 ml) whole milk, 1 tsp (5 ml) apple cider vinegar, salt and pepper