In German it is called Beifuss (Beifuβ) and is used when roasting fat Poultry such as Goose or Duck.
It is also growing in the USA and easily found in online stores.
When I was young my mother sent us down to the railroad tracks where it was found in abundance, before the flower buds opened. Gathered, brought home and all the leaves were picked off, that only the buds remained on the stalks.
As the time of the bud development was around St. John’s Day this plant is sometimes also referred to as St. John’s Plant.
Bundled and dried for use year round for festive duck or goose dinners.
A few sprigs stuck into the goose cavity before roasting, gave the bird(s) the special taste we were used to for the holidays.
It is said that that expression “to get goosed” or “is goosed” comes from this use of Mugwort.
I can not find it in any descriptions of the plant, but my Grandmother told me that the bitterness of the plant helps in digesting the fatty food. It makes sense as in Germany we used to drink a “Stomach Bitter” shot of booze/medicine after a fat dinner. Stomach Bitters where considered liquors made from herbs, like Underberg and even a Jaegermeister can fall in this category.