Beat together the butter, sugar, eggs, flour, baking powder, mixed spice and ground nuts in a bowl until smooth and creamy. Stir in the carrots and sultanas until evenly combined.
Divide the mixture evenly between 2 greased, baselined and floured 20 cm (8 inch) sandwich tins (see
Make the frosting. Beat together the cream cheese and butter in a bowl until smooth. Stir in the icing sugar and lemon juice, then use half to sandwich the cakes together. Spread the remaining icing over the top of the cake.