- Preheat oven to 350°F.
- In a large skillet, add the ground beef and onion over medium-high heat and brown the ground beef, breaking the meat apart well as it cooks.
- Drain grease, if needed, then add bouillon cube, water, brown sugar, apple cider vinegar, and Worcestershire sauce. Bring to a boil, then reduce heat and let simmer until liquid has evaporated.
- Place bottoms of the buns in a baking dish, and top with beef mixture. Place pickles on top, followed by cheese slices, and top with top of buns.
- In a small bowl, whisk together melted butter, brown sugar, Dijon mustard, and Worcestershire sauce and brush over buns.
- Cover baking dish with foil and bake 25 minutes. Enjoy!