Reserve Pan Juices

Transfer the turkey to a serving platter, and set it aside to rest while you make the gravy. Carefully pour the warm pan juices from the pan into a fat separator, and set aside. The fat will rise to the top as the liquid cools; the dark drippings, which are filled with flavor, will stay at the bottom near a low-slung spout, which will later pour the juice straight into a pan.

Deglaze Pan

Meanwhile, return the roasting pan to the stove top over medium-high heat. Carefully pour 1 1/2 cups Madeira wine into the roasting pan; bring to a boil, and use a wooden spoon to scrape off the caramelized and crispy brown bits that are stuck to the sides and bottom of the pan. The roasting pan should appear to be virtually clean when it is properly deglazed. These cooked-on bits carry the turkey's flavor right into the gravy.

Combine Flour and Giblet Stock

Warm the giblet stock over low heat. Place 3 tablespoons of flour in a glass jar that has a tight-fitting lid. Fit a wide-mouthed funnel in the top of the jar. Ladle 1 cup of the warm stock into the jar. Reserve the remaining stock in the saucepan, and keep warm over low heat.

Shake Jar to Make a Slurry

Close the jar tightly, and shake vigorously until all the flour is incorporated into the warm stock; this liaison is called a slurry. Combining the flour and stock before adding it to the gravy solves the problem of lumpy gravy.

Slowly pour the slurry into the roasting pan, stirring to fully incorporate. Cook over medium-high heat, stirring constantly, until the flour is fully cooked and all the traces of its raw, chalky flavor are gone, 2 to 3 minutes. Stir reserved warm giblet stock into gravy in roasting pan.

Add Separated Pan Drippings

Pour the pan drippings from the fat separator into the roasting pan, taking care to add only the dark drippings at the bottom. Discard the fat. Add rosemary, and stir well. Adjust seasoning. Cook over medium-high heat, stirring occasionally to thicken, until reduced to about 3 cups, 10 to 15 minutes.

Strain to Remove Solids

Place a fine sieve (or a strainer lined with lightly dampened cheesecloth) in a quart-size measuring cup or medium bowl. Pour gravy into the sieve or strainer. Use a wooden spoon to press down on remaining solids to extract all the juices; discard solids. Adjust seasoning. Gravy may be kept warm by placing the bowl in a saucepan containing 1 inch of barely simmering water. To serve, transfer to a heated gravy boat.