After roasting chicken, pour all drippings from pan into a fat separator or glass measuring cup. Let sit for 5 minutes. Fat will rise to top. Flavorful liquid will settle at bottom. You need ¼ cup (60ml) of fat for roux and about 2 cups (480ml) total liquid (combining drippings and stock). If not enough fat, supplement with butter. If not enough liquid drippings, use chicken stock.

Place roasting pan (or large skillet) over medium heat on stovetop. Leave about 2 tablespoons fat in pan, pour off excess. Heat until fat shimmers. Add ¼ cup dry white wine or sherry to hot pan. Liquid will sizzle immediately. Use wooden spoon to scrape bottom of pan vigorously. All dark, caramelized bits (fond) will dissolve into liquid. Let wine reduce by half, about 2-3 minutes. If not using wine, substitute with ¼ cup chicken stock.

Once wine has reduced, add reserved chicken fat (or butter) to pan. Let melt completely over medium heat. Fat should be hot but not smoking. Sprinkle ¼ cup all-purpose flour evenly over fat. Immediately begin whisking. Mixture will bubble and foam. Keep whisking steadily—you're coating every flour particle in fat. Cook roux for 3-4 minutes, whisking constantly. Color will shift from pale yellow to light tan to golden blonde. You'll smell toasted, nutty aroma. This is raw flour taste cooking out. Do not rush this step.

With whisk in one hand and warm chicken stock in other, begin adding stock very slowly—just a few tablespoons at a time. Whisk constantly as you pour. Roux will seize up and look thick at first—this is normal. Keep whisking. As you add more liquid, mixture will loosen and become smooth. Add stock in three or four additions, whisking thoroughly between each pour. Once all stock is incorporated, add reserved drippings (liquid from bottom of fat separator). Whisk to combine. Drop in fresh thyme sprigs.

Bring gravy to gentle simmer over medium heat. Don't boil aggressively—high heat can break emulsion. You want lazy bubble, just enough to steam and thicken. Simmer for 8-10 minutes, whisking occasionally. Gravy will thicken as starch granules continue to absorb liquid and swell. Flavors will concentrate. Thyme will infuse. To test for doneness, dip spoon into gravy and run finger across back. If line holds and doesn't run, gravy is ready. It should coat spoon in smooth, glossy layer.

Remove thyme sprigs. Place fine-mesh strainer over clean saucepan or serving bowl. Pour gravy through strainer, pressing gently with spoon to push all liquid through. This removes any flour clumps, bits of fond, or herb stems. Taste strained gravy. Add kosher salt and freshly ground black pepper to taste. If you want more depth, whisk in ½ teaspoon Better Than Bouillon. If gravy is too thick, thin with splash of stock. If too thin, return to heat and simmer 2-3 more minutes. Transfer to warm gravy boat or serving pitcher.