Preheat your oven to 180°c/160°c fan/gas mark 4
Grease and line 3x 20cm cake tins
To make the orange curd, place all the ingredients into a medium sized pan over a medium heat. Whisk for about 8-10 minutes or until the mixture thickens. Turn the heat down to a simmer and whisk for one more minute. Remove from the heat and cool completely.
To make the cakes, beat together the Lurpak®, sugar and eggs in a large bowl until the mixture is light and fluffy and doubled in size.
In a separate bowl, mix together the two flours, bicarbonate of soda and rosemary. Gently fold the flour mixture into the butter mixture making sure you don't knock out any of the air.
Gently fold the carrots into the cake mixture and divide the mixture evenly between the three tins. Bake in the oven for 25-30 minutes or until a skewer, when inserted into the middle of the cake, comes out clean. Leave to cool in the tins for 10 minutes and then turn onto a cooling rack.
To make the butter icing, beat the Lurpak® for about five minutes using an electric mixer. Add the icing sugar and vanilla extract and lemon zest and beat again until the mixture is fully incorporated. Slowly add the milk and beat until the mixture is smooth.
When the cakes have cooled down, take the first sponge and spread with a third of the buttercream and drizzle with half of the orange curd. Top with the second sponge and repeat with a third of the buttercream and the remaining orange curd. Top with the final sponge and spread with the remaining buttercream.