In a large skillet over medium-high flame,heat bacon drippings. Remove the brisket from the marinade and discard the onion and vinegar. Pat dry with paper towels. Place brisket in the skillet and brown well on each side. Remove and set aside; reserve bacon drippings.
To the skillet, sauté the remaining onions until deeply browned (add more bacon grease if necessary). Pour in 1/2 cup coffee and bring to a boil to deglaze the pan (scrape the bottom of pan to remove the browned bits).
Pour the onion coffee mixture into a large shallow baking dish. Place brisket on top of the onions and sprinkle liberally with salt and freshly ground pepper. Pour in the remaining coffee and water. Cover tightly with aluminum foil and place in oven.
Roast at 350°F for 30 minutes. Reduce oven temperature to 250°F and roast for an additional 4 hours or until meat is very tender.
Allow brisket to rest for about 20 minutes before slicing, then slice thinly across the grain.