Remove the silver skin and any thick, hard fat, leaving about ¼ inch of the softer fat cap intact. Pat dry with paper towels.

Spread the yellow mustard evenly over all sides of the brisket using a pastry brush or your hands.

Combine the kosher salt, brown sugar, black pepper, smoked paprika, chili powder, garlic powder, onion powder, cumin, and optional cayenne pepper in a small bowl.

Sprinkle the dry rub over all sides of the brisket. Press the seasoning firmly onto the meat.

Place the brisket fat-side up on a wire rack set inside a baking sheet. Refrigerate uncovered for 8–24 hours.

Preheat to 275°F. Insert an oven-safe probe thermometer into the thickest part of the brisket.

Place the brisket in the center of the oven. Bake until the internal temperature reaches 160°F, about 2 ½ to 3 ½ hours, depending on thickness.

Remove the brisket from the oven and place it on overlapping sheets of heavy-duty aluminum foil. Drizzle some of the rendered fat over the top, then wrap tightly and seal the seams.

Return the wrapped brisket to the oven and cook for another 2 to 3 hours, until the internal temperature reaches 200°F to 205°F. Begin checking for tenderness around 200°F.

Remove it from the oven when a thermometer or thin skewer slides into the thickest section with very little resistance. Keep it wrapped and rest for 30 minutes.

Carefully open the foil and reserve the juices. Cut the brisket against the grain into ¼-inch slices. Spoon some of the reserved juices over the meat before serving.

Tender brisket slices with a dark seasoned crust and cooking juices.