1.Preheat oven to 180°C/350°F. Grease deep 20cm(8-inch) round cake pan; line base with baking paper.
2.Beat butter, rind and sugar in small bowl with electric mixer until light and fluffy. Beat in eggs, one at a time (mixture might curdle at this stage, but will come together later).
3.Transfer mixture to large bowl. Stir in sifted flour, the milk and juice in two batches. Pour mixture into pan.
4.Bake cake about 50 minutes. Stand cake in pan 5 minutes before turning, top-side up, onto wire rack to cool.
5.To make lemon mascarpone frosting, beat cream, sifted icing sugar and rind in small bowl with electric mixer until soft peaks form. Fold cream mixture into mascarpone. Cover; refrigerate until required.
6.Split cooled cake into three layers; place one layer on serving plate, cut-side up. Spread with one-third of the frosting. Repeat layering process, finishing with frosting over top of cake.