Preheat the oven to 180°C/355°F and oil and line a 13 x 23cm loaf tin with greaseproof paper.
For the carrot cake: beat the eggs in a large bowl, then add the oil, brown sugar, cinnamon, nutmeg, grated carrot, raisins and chopped walnuts.
Sift in the rest of the dry ingredients and bring the mixture together using a wooden or large metal spoon until well combined. Pour the mixture into the prepared loaf tin, smooth the surface and bake in the oven for 1 hour 15 minutes, or until a skewer inserted into the middle comes out clean. If you’re using a ceramic baking dish then you’ll need to add 15 minutes to the cooking time.
Remove from the oven and allow the cake to cool in the tin for about five minutes before removing. Cool completely on a wire rack before serving.
For the orange blossom frosting: beat the cream cheese and butter together in a bowl until well combined. Add the icing sugar, orange blossom water and finely grated orange zest and mix until the frosting is smooth and thick. Using a palette knife, spread the frosting evenly over the cooled cake, dipping the knife into a bowl of hot water if the icing is hard to spread out.
Decorate with orange zest on top of the frosting.