Put the butter and sugar into a bowl and beat until pale and fluffy. Beat in the eggs one at a time, then add the elderflower cordial. Sift in the flour and gently fold together using a large metal spoon. The mixture should drop off the end of the spoon when tapped; if it doesn’t, add enough of the milk until it does.
Meanwhile, make the icing. Beat the butter until pale and fluffy. Sift in the icing sugar and beat again until smooth, scraping down the sides with a spatula to make sure the mixture is thoroughly combined. Finally, fold in the cream cheese – don’t overbeat the icing at this stage or it might become too soft.
Allow the cakes to cool in the trays for 5 minutes, then transfer to a wire rack and leave until completely cold.
To serve, cut each cake in half horizontally. Spread the icing on the bottom half and gooseberry jam on the top half. Sandwich together and dust with caster sugar.