My personal favorite is Chaga - Inonotus obliquus. This fungus can be found world wide in boreal forests containing yellow birch trees. It can be found on beech trees as well, and a few other species I cannor recall at this moment. I have harvested Chaga in Maine, Montana, and North Carolina USA, as well as in Tajikistan, and Mongolia. The way I process it is to “cook” it in a crock pot over night. I will use the same fist size hunk of Chaga for several brewings.