Warm the brisket. If it’s cold, reheat brisket gently in a skillet over low heat with a splash of water or broth.
Add a spoonful of BBQ sauce to moisten. You want it warm and juicy, not dry.
Prep the bread. Spread a thin, even layer of butter or mayonnaise on one side of each bread slice. This is the side that will hit the pan and get golden.
Assemble the cheese layers. Place one slice of bread, buttered side down, on a cutting board.
Lay down a layer of cheese, then the warm brisket, a drizzle of BBQ sauce if you like it saucy, optional pickles or onions, and a final layer of cheese. Top with the second slice of bread, buttered side up.
Heat the skillet. Set a nonstick or cast-iron skillet over medium to medium-low heat. Add a small pat of butter or a teaspoon of oil to help with color and crispness.
Grill slowly. Place the sandwich in the skillet.
Cook until the bottom is deep golden and crisp, about 3–4 minutes. Press gently with a spatula, but don’t smash the sandwich flat.
Flip and finish. Carefully flip. Lower the heat slightly if the bread is browning faster than the cheese is melting.
Cook another 3–4 minutes, until the second side is golden and the cheese is fully melted.
Rest and slice. Transfer to a cutting board and let it rest 1 minute. This helps the cheese settle. Slice in half on the diagonal for easy eating.
Serve. Add extra BBQ sauce for dipping.
A simple side of slaw or chips works perfectly.