Preheat the oven o 350 degrees Pat the brisket dry and sprinkle with 3/4 teaspoon salt and 1/2 teaspoon pepper. Heat the oil in a large dutch oven or heavy oven proof pot over medium-high heat until hot, but not smoking. Brown the meat well on all sides, about 10 minutes. Transfer to a platter. Add the onions and bay leaf to the fat in the pot and cook over medium heat, stirring occasionally, until the onions are golden, 10-12 minutes. Remove from the heat and transfer half the onions to a bowl. Set the brisket over the onions in the pot, then top with the remaining onions. Add the beer, vinegar, and bouillon cube. The liquid should come halfway up the side of the meat; if it doesn't add water. Bring to a boil. Cover the pot and braise in the oven until the meat is for tender, 3-4 hours. Let the meat cool in the sauce, uncovered, for 30 minutes. Transfer the brisket to a cutting board. skim off any fat from the sauce, remove the bay leaf . Slice across the grain and serve with the sauce.