Preheat the oven to 180C/350F/Gas 4. Grease and line a 9in/23cm cake tin.
Beat the eggs and sugar together in an electric mixer for five minutes, or until light and fluffy. Add the vanilla, lemon juice and zest.
Meanwhile bring the milk and butter to the boil. Whilst the mixer is on a medium setting, gently pour in the milk mixture.
Turn off the mixer and fold in the dry ingredients until just combined. Spoon the mixture into the tin and cook for 50-55mins. Set aside to cool. (The sponge is cooked through when a skewer inserted into the centre of the cake comes out clean.)
For the frosting, beat the sugar and butter together for five minutes or until light and fluffy. Add the vanilla and cream and continue to beat until well combined.
Fill a piping bag with the frosting mixture. Starting from the inside pipe the frosting in a spiral pattern. Smooth over the middle of the cake frosting with a palette knife or the back of a spoon, leaving a piped edge.
Place the pistachios and candied lemon zest on top and serve.