Smoked BBQ Brisket

• 1/2 cup ancho chili powder
• 2 tablespoons paprika
• 1 tablespoon ground cumin
• 1 tablespoon dry mustard
• 1 tablespoon kosher salt
• 2 teaspoons cayenne
• 1 trimmed brisket with a layer of fat at least 1/4-inch thick, about 5 to 6 pounds
• Dark Beer Mop, recipe follows

Dark Beer Mop:

• 1 large red onion
• 4 cloves garlic
• 2 serrano chiles, chopped
• 4 bottles of dark beer
• 1/4 cup dark brown sugar
• 2 bay leaves
• Salt and freshly ground pepper