In a 10- to 12-inch frying pan over medium-high heat, frequently stir onion in butter until onion is limp and pale gold, about 5 minutes. Add nutmeg and flour and stir until golden, about 2 minutes.
Remove pan from heat. Gradually whisk in broth, cream, and wine until smooth. Return to high heat and stir until boiling. Reduce heat; simmer gently, stirring often, until mixture is reduced to about 2 cups, about 10 minutes.
Skim fat from drumstick crown roast drippings and discard. Scrape juices and any browned bits into gravy; turn heat to high and stir until boiling vigorously. Pour into a gravy boat or small serving bowl.
Nutritional analysis per serving of gravy (not including drippings).