Ginger Sponge

From 1922:

One egg, small cupful of treacle, small cupful sugar, small cupful thick milk, tablespoonful butter, and a little spice or nutmeg, a dessertspoonful ground ginger, half teaspoonful carbonate of soda, 2 cupfuls of self-raising flour. Bake in a fairly moderate oven for 20 or 25 minutes in greased sandwich tins. When done turn on powdered paper, then mix icing sugar and vanilla and a little butter. Mix well for filling, and use chocolate icing for dressing, then finish with cocoanut.