The smartest strategy is to make it ahead, in stages, as time allows.
Sprinkle with flour, whisking until smooth.
Cook, whisking constantly, 2 minutes.
Credit: Greg DuPree; Prop Styling: Kay E. Clarke; Food Styling: Torie Cox
Add warm broth in a slow, steady stream, whisking constantly.
Cook, whisking often, until gravy comes to a simmer and thickens, 6 to 9 minutes.
Remove from heat, and let cool 30 minutes.
Pour into a bowl or jar; cover and refrigerate up to 3 days.
To serve, reheat gravy over low.
Stir in cream, sherry, thyme, pepper, and salt.