In a medium sized pan add olive oil, minced onion and salt (1). Cook over medium heat, stirring occasionally until the onions are caramelized (2). Add the Chocolate Ancho Rub (3) and stir for about 30 seconds, to toast the spices. Add the molasses and stir another 15 seconds (4) to combine, deglazing with the stout beer (5); stir well, helping lift off any of the fond on the bottom of the pan. Add malt or cider vinegar and tomato sauce, keeping the heat to medium, stirring while cooking for about 25 minutes.
The sauce should be thick, dark brow, but not burnt. Add the shot of espresso and transfer the sauce to the pitcher of a blender and puree for about 1 minute or until smooth. Transfer the sauce to a pint size jar (6) and use with the Smoked Beef Brisket with Chocolate Ancho Rub (7).