I stumbled upon this cake when I realised I had no castor sugar. I used honey buttercream and a little jam for the filling but you could replace the honey with a citrus zest and vanilla essence for a fresher, less sweet cream.
Beat the butter, granulated sugar and icing sugar in a large mixing bowl with a wooden spoon until smooth.
Gradually add the eggs to the creamed butter mixture and beat until it's as smooth as it can be. I found mine looked as though there were lots of little lumps but in the next step it smooths out perfectly.
Gradually add the flour, folding in gently. Pour into a 23cm round cake tin.
Bake in the centre of the oven at around 170 C / Gas 3 for 25 to 30 minutes or until a knife can be pulled out clean. Cool cake completely.
Cream together the butter, sugar and honey for the buttercream. Pop in fridge for 15 minutes.
Once cake is cool, slice horizontally and layer with jam, if desired, and the buttercream. Add additional buttercream to the top, if desired.