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".
- 1945  At the tea, Barbara Walker assisted the little hostess in cutting the friendship cake, and there were favors and ice cream shaped like Christmas trees for all. 
- 1984  Baking Friendship Cake is popular in many parts of Ontario these days and finding ways to use the leftover starter is causing problems for economy minded cooks. 
- 1987  Dessert is friendship cake, a fruit cake made with ferment passed from one friend to another. 
- 1991  What a friendly bunch Province readers are: We received almost two dozen responses to our request for a friendship cake recipe. 
- 1992  Mrs. T. Metz of Mississauga requested a recipe for Friendship Cake. The "starter" and the recipe are passed along to a friend, who can then begin another batch. Using the starter, fruit and sugar are added every 10 days. After 30 days, the fruit is used to make cakes and the liquid is divided and passed along to friends as new starter with a copy of the recipe. 
- 1993  Use one to make Amish friendship cake, one for your use another time, and give two to friends, along with the cake recipe. 
- 1998  To make a friendship cake, the cook ferments fruit (peaches, pineapples, cherries, pears, apples, etc.) for thirty days (hence, the other name, thirty-day cake). One makes enough of the fermented fruit to pour off a few cups of its juice to give to friends as a starter. This fermented base is thus passed around a community from friend to friend, just as sour-dough starter was shared among pioneer bread-makers.
- 1999  On Prince Edward Island, friendship cake or 30-day cake was popular. The cake was made with fruit, such as peaches, pineapple, cherries, pears and apples, that was fermented for 30 days. Enough juice was made so that some could be poured off and given to friends as starter for them to make their own friendship cake. 
- 2007  Then there was the crown roast of wieners provided by one of our (former) columnists, and the dreaded friendship cake that went on and on, ad infinitum, until I declared it off-limits.