Preheat oven to 160ºC (320ºF). To make the lemon topping, beat the cream cheese, sugar and lemon juice in an electric mixer and beat for 5–6 minutes or until smooth. Set aside.
Place the flour, sugar, baking powder, eggs, milk, melted butter, sultanas, mixed spice and carrot in a large bowl and mix until well combined. Lightly grease and line the base of 2 x 22cm-round cake tins. Divide the mixture evenly between the tins and cook for 1 hour and 15 minutes or until cooked when tested with a skewer.
Allow to cool in the tins for 5 minutes. Turn out onto wire racks to cool completely. Place one cake on a serving plate and spoon over lemon filling. Top with the other cake and dust over icing sugar to serve. Serves 10–12.