Step 1

Slice off the top 1 to 1 1/2-inches of the loaf of bread using a bread knife. Cut around the perimeter of the interior crumb, making sure not to break through the bottom crust, then use your hand to lift out the excess bread from the inside, leaving you with a hollow bread boat.

Step 2

Spread beans on bottom of bread boat, followed by carnitas, salsa, cheese, pickled onions, and sliced jalapeños. Close sandwich.

Step 3

Wrap sandwich tightly in aluminum foil or butcher's paper, then place in between two stiff cutting boards. Place a heavy weight on top (about 40 pounds), press down firmly to flatten sandwich, then let rest under the weight for at least 4 hours and up to overnight (keep an eye on the sandwich to ensure that it is pressing evenly).

Step 4

When ready to eat, adjust oven rack to center position and preheat oven to 375°F. Remove weights, slice sandwich into four to six pieces through paper or foil with a bread knife, unwrap, and transfer to a rimmed baking sheet, pressing the pieces back together to form a full sandwich shape. Place in oven until hot and cheese has melted, about 15 minutes. Serve immediately.