A paper at a 2002 conference in Turku, Finland, quotes an interesting report from 1937:

There was something they called Good Friday whipping. Crazy youngsters in disguise with masks and ugly clothes went around the whole neighbourhood in big groups…

They went into every house and everybody, especially young women, were supposed to get whipped with a big birch rod or with twigs. Some were satisfied with beating over the fur rug on the bed. Others took it more thoroughly.

Old people told that one or the other who had an especially bad tongue got a spanking on their bare bottom. But otherwise this was usually done just for fun.

Girls, bent over fur rugs on beds to be birched thoroughly on their bare behinds? Sure beats handing over chocolate eggs as an Easter tradition!