⅓cup (40 g)cornstarch(arrowroot may be used in substitution, but hasn't been tested)
salt & pepper to taste
Make the Turkey Stock
Preheat the oven to 375° F.
Place turkey wings, carrots, celery, onions, and garlic in a large Dutch oven or pot. Bake, uncovered, for 2 hours.
Remove from the oven and add water. Bring to a boil and reduce to a simmer. Simmer for 1 hour, uncovered, skimming any foam that collects on the surface.
Strain the stock over a large mesh sieve that's been lined with cheesecloth (a coffee filter will also work in a pinch). You should have about 4 cups of stock. Refrigerate for at least 2 hours, preferably overnight. When set, remove any fat that's accumulated on top with a spoon. At this point, the turkey stock can be kept in the fridge for a few days or frozen for several months before making the gravy.
Make the Gravy
When ready to make the gravy, melt the butter in a large skillet or saucepan. Add the cornstarch and whisk continuously for about 1 minute. Whisk in the turkey stock, which will have gelled and will need to melt again.
Bring the gravy to a boil and reduce to a simmer. Simmer and whisk until the gravy thickens, about 5 minutes. If it's too thick, you can add water to desired thickness. Add salt and pepper to taste. Store in fridge for a few days or freezer for a few months.