Preheat your oven to broil, positioning the top oven rack about 6 inches from the broiler.
In a large, oven-safe skillet over medium heat, add the ground beef, diced onion, light brown sugar, garlic powder, kosher salt, and black pepper. Stir and cook until the beef is browned and fully cooked, breaking it up as it cooks. Drain any excess grease if necessary.
Stir in the beef broth, ketchup, and mustard, making sure everything is well combined.
In a small bowl, whisk together the cornstarch and water until smooth. Pour this mixture into the beef and stir, cooking until the sauce thickens.
Remove the skillet from the heat and stir in 1 cup of shredded cheddar cheese until fully melted.
Sprinkle the remaining shredded cheese over the top.
Place the skillet under the broiler and cook for 3-5 minutes, or until the cheese is melted, bubbly, and slightly golden.
Serve the dip warm with toasted baguettes or bagel chips.