In a small bowl, whisk together the mustard and worcestershire. Set aside.
1/4 cup dijon mustard, 2 Tablespoons worcestershire sauce
In another small bowl, whisk together the brown sugar, paprika, salt, garlic powder, onion powder, and black pepper. Set aside.
1/4 cup brown sugar, 2 Tablespoons smoked paprika, 1 Tablespoon Morton kosher salt*, 1 Tablespoon EACH granulated garlic & onion powder, 1-2 teaspoons fresh cracked black pepper
Line a baking sheet with foil. Place the trimmed brisket on the foil, noting the direction of the grain for slicing later. Rub the mustard mixture all over the brisket. Pat the dry rub into the mustard mixture on all sides of the brisket so it is completely coated. Turn the brisket fat cap side up.
3 pound brisket flat, trimmed (1/4 inch fat cap)*
Wrap the brisket tightly with foil. Transfer it to the refrigerator to marinate for at least 2 hours or up to overnight. When ready to cook, remove the brisket from the refrigerator and place it, still wrapped in foil, on a wire rack in a roasting pan. Preheat the oven to 250°F (120°C) and let the brisket rest at room temperature for about 30 minutes. Insert a meat probe into the thickest part of the brisket. Fill the roasting pan with about 1 inch of hot water (the water should not touch the brisket). Carefully transfer the pan to the oven and bake for approximately 4 hours, or until the internal temperature reaches about 185°F (85°C). In general this will take about 1 hour and 15 minutes per pound. Place the pats of butter across the top of the brisket.
4 Tablespoons unsalted butter, sliced
Continue baking for another 30 minutes to 1 hour, or until the internal temperature reaches 195°F (90°C).
Let the brisket rest on a cutting board, loosely tented with foil, for about 30 minutes. After resting, slice the brisket against the grain using a serrated knife. Serve with barbecue sauce.
barbecue sauce, for serving