01 -
In a large skillet over medium heat, melt the butter or heat the vegetable oil. Add the diced onion and sauté until translucent, about 3 to 4 minutes. Add the ground beef, breaking it apart with a spoon, and cook until well browned.
02 -
Stir in the yellow mustard, Worcestershire sauce, and beef broth. Season generously with salt and pepper. Allow the mixture to simmer for 5 to 7 minutes, stirring occasionally, until most of the liquid has evaporated but the filling remains moist.
03 -
Spoon the loose beef mixture onto toasted buns. Top with your choice of pickles, cheese, mustard, ketchup, or diced onions. Serve immediately while hot.