You will need some unusual ingredients to make this, notably sassafras roots. If you happen to live in the United States or Canada east of the Great Plains, you are in luck: Sassafras grows everywhere in that region. If you don’t live there, or don’t feel like foraging for your own sassafras, you can buy sassafras root bark online. The burdock in the recipe grows all around you as a weed. Otherwise, many good supermarkets have burdock in the produce section: They are long pale, skinny roots often sold under their Japanese name “gobo.” If you absolutely cannot get your hands on burdock, use dandelion roots. The root beer will be different, but still fine.