Heat the skillet over medium-high heat for about 1 minute.

Add the diced onion and cook for 2 minutes, stirring occasionally, until softened.

Add the ground beef and break it into small crumbles, cooking for 3 to 4 minutes until browned.

Tilt the skillet and carefully drain off excess grease, leaving just enough to coat the pan.

In a small bowl, whisk together garlic powder, onion powder, salt, and black pepper.

Sprinkle the seasoning mixture over the meat, then pour in beef broth, Worcestershire sauce, and mustard, stirring to combine.

Reduce heat to medium and simmer for 3 to 4 minutes, allowing the liquid to reduce and flavors to concentrate.

While the meat simmers, butter the buns and toast them face-down in a separate skillet over medium heat for 1 to 2 minutes per side.

Assemble the sandwiches by piling the meat onto the bottom buns, adding desired toppings, and capping with the top buns.