Mix together the salt, black pepper, cayenne and crushed garlic, and rub all over your brisket (more heavily on the meatier side but also a bit on the fat side as well). Allow the brisket to come to room temperature.
In a large roasting pan, add the slivered onions, soy sauce, Worcestershire sauce, 1/4 cup of the liquid smoke, black coffee, apple cider vinegar, and half the sliced jalapeños.
Place the brisket in the pan, fat side up, and sprinkle the remaining jalapenos on top of the brisket.
Cover the pan tightly with foil, and bake in the oven for 5 hours or roughly 1 hour and 15 minutes per pound.
Take the brisket out of the oven, and it should be tender to the touch. Let it sit out of the pan for half an hour, and then trim the fat on top and slice against the grain. If you desire a gravy, the pan juice is a fine, fine topping.