Pre-heat your oven to 160C Fan/180C/350F/Gas Mark, and grease and line two 8 inch sandwich tins (that are at least 2" deep)
In a large bowl, stir together the self raising flour, wholemeal flour, baking powder, bicarbonate of soda, mixed spice, cinnamon and light brown sugar
In another bowl or large jug, whisk together the vegetable oil, eggs, orange zest and orange juice. Then add it to the flour mixture and whisk everything together
Mix in the grated carrot, chopped pecans and sultanas
Divide the mixture evenly between the cake tins, use scales for accuracy
Bake for 40-45 minutes until golden brown and a thin skewer inserted in the centre comes out clean. Remove them from the tin and leave them to cool on wire racks
If the cakes have domed on top, level them off with a cake leveller or a knife
To make the frosting, use an electric mixer to beat the butter on it's own until soft and creamy
Add the icing sugar, and mix in until well combined
Add the cream cheese and the vanilla extract, mix until just combined and smooth
Place one of the sponges onto a plate or cake stand and spread or pipe some of the frosting over it
Top with the second sponge, then pipe or spread the remaining frosting on top
Decorate with fondant carrots and chopped pecans
Store any leftovers in the fridge for up to 3 days