01 - In a medium saucepan over medium heat, melt beef fat or unsalted butter.
02 - Add finely chopped onion and cook for 3 to 4 minutes until softened and translucent.
03 - Stir in minced garlic and cook for 30 seconds until fragrant.
04 - Sprinkle all-purpose flour over the mixture and cook, stirring constantly, for 2 minutes to create a roux.
05 - Gradually whisk in beef stock, ensuring the mixture remains smooth and free of lumps.
06 - Add Worcestershire sauce, freshly ground black pepper, and salt to taste, then bring to a gentle simmer.
07 - Reduce heat and simmer for 10 to 15 minutes, stirring occasionally, until the gravy reaches desired thickness.
08 - Whisk in Dijon mustard and stir in chopped fresh parsley just before serving, if desired.
09 - Optionally, strain the gravy through a fine mesh sieve for a smoother texture.
10 - Pour hot gravy into a gravy boat and serve immediately.