While the turkey rests on the cutting board, make the gravy: Use a fine-mesh strainer to strain the pan drippings into a medium bowl, leaving behind any browned bits, or "fond," stuck to the pan. Press down on the solids to get as much liquid as possible into the bowl; discard the solids. Pour the liquid into a measuring cup or a fat separator. After all the fat rises to the top, ladle the fat into a bowl and reserve. You should be left with about 1 cup of jus. Place the roasting pan across two burners over medium-low heat. Add the shallots and 2 tablespoons of the reserved turkey fat; sauté until the shallots are soft, 2 minutes.
Add the wine and stir, scraping up the fond from the bottom of the pan. Bring to a simmer; continue scraping and simmering until the mixture has reduced to about a cup, 3–5 minutes. Once the wine mixture has reduced to 1 cup, add the reserved jus and enough turkey or chicken stock to bring the total amount of liquid to 4 cups; stir to combine. Strain the liquid through a fine-mesh strainer set over a medium bowl; discard solids. Wipe out any remaining solids in the pan.
Make a roux: In the roasting pan, melt the butter over medium-low heat. When melted, sprinkle in the flour and whisk it into the butter until the flour is completely incorporated and no longer raw, 1–2 minutes. When the flour begins to bubble, ladle in a small amount of the jus mixture at a time, around ½ cup per addition, whisking continuously. When the mixture looks like a paste, turn the heat to medium, and continue adding more liquid, a ladle or two at a time, and whisking. Small additions of liquid and continuous whisking are the keys to smooth gravy. Repeat the process until all the liquid has been incorporated and the gravy is thick, smooth, and velvety. (Tip: If gravy has any lumps at the end, pour it through a fine-mesh strainer to remove them.) Season to taste with salt and pepper. Pour into a gravy boat or bowl and serve immediately.