In a large cast-iron skillet, melt butter over medium heat. Add flour, whisking to combine. Slowly add stock, whisking to combine; simmer, stirring frequently, until thickened, 6 to 7 minutes. Add whiskey, Worcestershire, salt, vinegar, and pepper; cook for 3 more minutes. Serve hot.
Recipe by Southern Cast Iron at https://southerncastiron.com/beef-wellington-with-whiskey-gravy/