Add the ketchup, mustard, Worcestershire sauce, vinegar, salt, and pepper into a bowl. Stir until well-combined. Transfer the mixture into a jar, seal well, and refrigerate for at least 30 minutes.
Notes
For best results, prep all ingredients before starting this a1 steak sauce. Taste as you go and adjust seasoning or sweetness to your preference. Store leftovers properly and enjoy within a few days for the best texture.