Broilers vary in heat intensity; move the rack to a lower position if the chicken is browning too quickly, or to a higher rack if too slowly. Remove items from the baking sheet as done, if they're cooking unevenly.
Mugwort (Artemisia vulgaris) is one of about 300 species in the Artemisia genus. It's what you want for this soup; the others may be too bitter. Watercress will also work; although the soup won't taste the same, it will still be delicious.
Excerpted from "Foraged Flavor: Finding Fabulous Ingredients in Your Backyard or Farmer's Market, with 88 Recipes" by Tama Matsuoka Wong, Eddy Leroux and Daniel Boulud.