For the sponge • g/1lb 2oz salted butter, at room temperature, plus extra for greasing the tins • g/1lb 2oz caster sugar • large free-range eggs, lightly beaten • vanilla extract • g/1lb 2oz self-raising flour, plus extra for dusting the tins • For the buttercream • g/1lb 2oz salted butter, at room temperature • kg/2lb 4oz icing sugar • vanilla extract • milk • To decorate •