For a sauce worthy of your bird, you need pan drippings. The turkey fat and those delicious browned bits are the building blocks of flavor.
Place the roasting pan with the drippings from the turkey over 2 stovetop burners and heat over medium. When the drippings are hot, add 1 cup stock. Cook, stirring and scraping up the browned bits from the bottom of the pan. Pour into a heatproof measuring cup. Refrigerate until the juices separate and the fat begins to firm up, about 30 minutes. Skim the fat from the top of the drippings.
In a medium saucepan, melt the butter over medium-high heat. Whisk in the flour. Reduce heat to low and whisk the butter and flour until pale golden and bubbly, about 2 minutes. Whisk in the drippings, then the remaining 1 cup stock. Cook over low heat, stirring occasionally, until the gravy thickens, 1 to 2 minutes. Season with kosher salt and pepper.