Trim off ¼ inch layer of fat from the top of the brisket. Remove the big chunk of fat that’s running through the brisket. Remove any silver skin from the bottom of the brisket. You can ask your butcher to clean it for you.
In a bowl, mix the salt and pepper. Liberally season brisket evenly on both sides. Transfer to a large baking pan, cover, and set out at room temperature for 1 hour.
While the brisket is marinating: Turn on the heat to medium in a medium pot; add the ketchup, beer, Worcestershire sauce, brown sugar, salt, pepper, and cayenne; stir to combine and bring to a boil. Once boiling, reduce heat to low, cook for 5 minutes, stirring occasionally. Taste and adjust seasoning.
Preheat the oven to 250°F, add the water to the baking pan, cover the brisket loosely with foil, and bake for 3 hours. Remove the foil and continue baking for 2-3 hours uncovered, until brisket internal temperature is 180-190°F. If you don’t have an instant-read thermometer, a small knife or fork should be able to easily pierce the brisket. Cover the brisket loosely with foil and cool for 30 minutes. After the brisket has rested, slice, and serve immediately with bbq sauce, white bread, pickles, and onions.