Preheat oven to 250°F. Combine BBQ sauce and low-sodium beef broth in a measuring cup. Place brisket slices in a single layer in an 11x7 baking dish. Then, pour the prepared liquid over. Cover the dish tightly with aluminum foil and heat in the oven for 20-30 minutes.
Combine room temperature unsalted butter and Hellmann's Garlic Aioli in a small bowl. Then, spread one tablespoon of the mixture over one side of each piece of bread. Heat a large cast-iron skillet over medium heat.
Place one slice of prepared bread, buttered side down, onto the skillet. Then top the bread with two slices of extra sharp cheddar cheese.
Place the heated brisket in a single layer on top of the cheese, then drizzle with additional BBQ sauce. Sprinkle two tablespoons of French's Crispy Fried Onions over the sauce-covered brisket. Top with two slices of pepper jack cheese on top of the fried onions. Then, place another slice of the prepared bread, buttered side up, on top of the cheese.
Cook for 3-4 minutes, until the underside is golden brown. Carefully flip the sandwich over and cook for an additional 3-4 minutes. Remove from the pan and transfer the finished sandwich to a wire cooling rack for a few minutes before serving.
Repeat steps 3-6 to make the second sandwich.
Yield two Ultimate BBQ Brisket Melt Sandwiches