Also known as "Cattle Drive Sauce", this is another innovation from my neighbors to the east. By the late 1870's, condiments such as ketchup, Worcestershire sauce and vinegars were available in cans or bottles - a blessing to the chuckwagon cooks of the era. There'd be biscuits, beans and coffee for breakfast and then the leftover coffee went into a large jar. In the evening that day-old coffee would come out and be used in this Black Jack sauce. You can make this a thin sauce to dip or a thicker sauce to slather on top of the steak - depending on how long you let it reduce
In a saucepan over medium high heat, combine the onions, coffee, Worcestershire sauce, ketchup, vinegar, brown sugar, jalapeños, chili powder, salt, and garlic. Stirring often, bring the mixture to a boil and then reduce the heat. Stirring regularly, simmer the sauce until it reduces by 1/2, about 25 minutes. Strain the sauce or puree it in a blender or food processor. Allow it to cool to room temperature and then refrigerate it for 8 hours to allow the flavors to fester. Refrigerate between uses.