n. — Food
a fruitcake made with a starter culture that is often shared between friends; also "thirty-day cake".
The term friendship cake describes "a fruitcake made with ferment passed from one friend to another" (see the 1987 quotation); both the starter culture and the recipe are given to friends or neighbours as "thoughtful gifts" (see the 1991 and 1996 quotations). The cake itself takes 30 days to make, adding ingredients (e.g. peaches, pineapples) at prescribed intervals along the way, hence the term "thirty-day cake" (see the 1992 & 1999 quotations). The term is used in the US and the UK, among other places. Historically, it has been popular on Prince Edward Island (see the 1999 quotation, DPEIE reference), yet for lack of new evidence it falls short of being qualified as a historical regionalism.
See also ITP Nelson, s.v. "friendship cake", which is marked "Prince Edward Island" and DPEIE, s.v. "friendship cake".