Carrot cake with cinnamon frosting

• zest and juice 1 orange
• 50g sultanas
• 150ml sunflower oil , plus extra for greasing
• 2 eggs
• 140g soft light brown sugar
• 85g wholemeal self-raising flour
• 85g self-raising flour
• 2 tsp each ground cinnamon and ground mixed spice
• 1 tsp bicarbonate of soda
• 140g carrots , coarsely grated
• 50g walnuts , chopped, plus a few halves to decorate

FOR THE ICING

• 200g soft cheese
• 50g butter , softened
• 85g icing sugar , sifted
• pinch ground cinnamon