Heat olive oil in a large skillet over medium-high heat. Add onion and season with salt and pepper. Stir until onions become translucent, about 4 minutes.
2. Add ground beef. Season with salt and pepper and stir breaking up until meat is no longer pink.
3. Add garlic and Worcestershire and stir until fragrant, about 1 minute. Add bone broth. Bring to a boil. Reduce heat and simmer uncovered for about 30 minutes or until broth is reduced almost completely.
4. Top the buns with mortadella slices (if using), ground beef, diced pickle, and cheese slice.
High fives to our pal Molli Pletcher for this creative and easy dish.