How to Make Gravy
Step 4: 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.