The Everyday Maven and AllRecipes both have recipes for making A1 Steak Sauce at home that are rated highly by website users. The Everyday Maven utilizes more spice and calls for fresh produce like onion, lemon and garlic.
To make the Everyday Maven's recipe, combine 1/2 cup water, 1/2 cup balsamic vinegar, 1/4 cup Worcestershire sauce, 1/4 ketchup and 1/4 cup mustard in a saucepan. Add spices to the saucepan, including 1/4 cup raisins, 1/2 teaspoon of both celery seeds, salt, 1/4 teaspoon black pepper and a small pinch of cayenne pepper. Finally, add 2 smashed cloves of garlic and 1/8 of an onion in small chunks. Squeeze the juice from the orange into the saucepan, then bring to a boil and reduce to a simmer for six minutes. Strain through a fine mesh strainer, simmer and allow the sauce to cool before serving.
To make the AllRecipes' A1 steak sauce recipe, mix together 1 1/4 cups ketchup, 2 tablespoons each of yellow mustard and Worcestershire sauce, 1 1/2 tablespoons of apple cider vinegar, several drops of hot pepper sauce and 1/2 teaspoon each of salt and ground black pepper. Transfer all of these ingredients to a jar, and refrigerate the mixture until needed.