Because we always cook our turkey on a smoker, I never have pan drippings for gravy. I have always made a big batch of turkey stock in advance of Thanksgiving and used it as a basis for my gravy and for moistening the dressing. The recipe for the stock is straight from epicurious, just omit the onions to make it free of FODMAPs. You can do this many days ahead and freeze it. Sweet rice flour is a very finely milled flour. It works almost as well as regular flour for thickening. I prefer it to gravies thickened with cornstarch. I can find it my grocery store in the Asian foods section.
8 tablespoons butter
8 tablespoons sweet rice flour
1 quart turkey stock, warmed
Melt the butter in a saucepan over medium heat. When the foam starts to subside, dump in the flour and whisk vigorously to get it combined with the butter. When it is all incorporated, whisk in the stock. Keep whisking while bringing the gravy to a simmer. Simmer it over low heat until nicely thickened. Season with salt and pepper.