Set a large skillet over medium-high heat. Cook the ground beef and onion, breaking up the meat, until the beef is no longer pink and the onion has softened, about 5 to 6 minutes. Drain excess fat if needed.

Reduce heat to medium. Stir in the garlic and cook 30 seconds. Add the BBQ sauce, ketchup, Worcestershire, brown sugar, vinegar, salt, and pepper. Stir to combine.

Simmer over medium-low heat for 8 to 10 minutes, stirring occasionally, until the sauce reduces and thickly coats the beef.

Brush the cut sides of the buns with butter or oil and toast until golden, about 1 to 2 minutes. Pile the saucy beef onto the buns and serve immediately.