Classic carrot cake

Name: Classic carrot cake
Ingredients: vegetable oil, for the tins; 200g butter, softened; 200g light muscovado sugar; 4 eggs; 150g self-raising flour; 50g rye or spelt flour (optional – use a total of 200g self-raising flour if you prefer); ½ tsp bicarbonate of soda; 1 tsp ground cinnamon; ¼ tsp mixed spice; 250g (about 3 medium) carrots, trimmed and coarsely grated; 75g raisins or sultanas; 75g light muscovado sugar; 100g pecans; 150g butter, softened; 150g icing sugar; 340g full-fat soft cheese; ½ lemon, zested