Crumble ground beef and minced onion together in a large skillet over medium-high heat. Cook until most of the outside is browned, but there is still some pink.
Add pickle juice, root beer, garlic, and Worcestershire to the pan. Bring to a boil, then cover and reduce heat to medium-low. Cook for 20 minutes. The liquid should simmer, but not boil.Remove lid and continue cooking until most of the liquid is absorbed. Add salt and pepper and cook an additional minute, then serve.
When ready to serve, butter your buns and place on a baking sheet, cut side up. Put baking sheet on the top rack of your oven, and broil on high for 1 minute, or until the buns are lightly toasted. Scoop meat onto the buns and add desired toppings.