To me, shepherd's pie is often all about "leftovers" so that should be fine. What kind of
mushrooms do they have--just regular button or others?
I was interested in the "organic" growing of mushrooms and looked at this site (in CA but a similar one was posted in PA).
There is not a big difference in how organic and conventional mushrooms are grown. Synthetic pesticides are not allowed in organic production. The main difference is the nitrogen used in the growing process. For conventional mushrooms, Urea, a synthetically produced input material is used for nitrogen. Organic mushrooms utilize fresh (or dried) chicken manure for nitrogen in phase 1 of the composting process. Mushrooms are grown indoors and the compost is pasteurized prior to planting.