Potatoes arrived in Europe from South America no earlier than the 16th century. My question was about how the "pie" was made prior to that ... and the answer was, with a grain-based crust and sweetened with fruit.
My mother, who is from Northern Ireland, made shepherd's pie with ground beef. In the U.S. from the 1940's on (at least) lamb was too expensive. We sometimes had leg-of-lamb at Easter, or when the Navy Commissary mysteriously had a batch of lamb-legs in stock.
In the 60’s my lamb-loving grandparents would drag us to Greek festivals in Chicago every weekend in the summer so much so I thought that’s what all American’s did on the weekend! It was until the 2nd grade I learned it was just us!!
In the winter my grandfather made a BBQ spit in his garage to roast lamb. My grandparents reeked of garlic!! Lordy, could my grandparents cook.