So far as explaining my letter to Kris, I have listed the ingredients which may use for preparing prasadam but these various varieties of foodstuffs may be prepared either in the given recipes or if you like you may invent nice new formulas for offering. The important thing is that your preparations be palatable for Lord Krishna and that the ingredients be within the groups of ingredients already listed. You have asked me about sassafras and yes, it may be offered. Mushrooms are generally not offered, but there is no prohibition, there is no harm in them.
Letter to Harer Nama, 1 December, 1968