3 cups chicken broth
3 tablespoons Worcestershire sauce
3 tablespoons spicy brown mustard
1 teaspoon salt
1 teaspoon ground black pepper
¼ cup yellow mustard, or as needed
12 hamburger buns, split
24 dill pickle slices
Heat a large skillet over medium-high heat, and cook and stir until the beef is crumbly, evenly browned, and no longer pink. Drain and discard any excess grease. Stir in the chicken broth, Worcestershire sauce, brown mustard, salt, and pepper. Bring to a boil, then reduce heat to low, and simmer uncovered until the liquid has evaporated, about 30 minutes. Meanwhile, preheat an oven to 300 degrees F (150 degrees C). Spread the desired amount of yellow mustard on the top half of each bun. Place 2 pickle slices on the bottom half, then spoon 2 to 3 tablespoons of the ground beef mixture over, and top with the other half of the bun to make a sandwich. Repeat until all the sandwiches are complete. Wrap each sandwich individually with aluminum foil and place on a baking sheet. Bake in the preheated oven until the bread is warmed through, about 10 minutes.