From 1922:

Make a Swiss roll with 1 oz. of butter, creamed with a teacupful of castor sugar, add 2 eggs, well beaten, then a teacupful of sifted flour and a teaspoonful of baking powder. Bake in a buttered and papered tin, till a pale brown, turn out on a piece of sugared paper, spread with warm jam and roll up quickly. When cold, cut off each end crossways, representing a log and pour over some icing made by dissolving a cake of chocolate in some hot water, then stir in enough icing sugar so it will run smoothly. Decorate with some chopped Pistachio nuts, to represent moss.