From 1922:
A plain cake: A quarter of a pint of greengage puree, ¼ pint (whipped) cream, ¼ pint milk. Take a slice from the top of a plain round cake, and scoop out the inside of the cake, taking care not to cut through the sides or bottom. Mix together the milk and greengage puree (made by rubbing ripe greengages through a sieve), and fill the cake with the mixture. Decorate the top with the whipped cream passed through a rose forcing pipe.