Preheat your oven to 180°C (160°C fan)/Gas Mark 4. Grease and line two 8-inch (20cm) round cake tins with baking parchment.
In a large bowl, sift together the plain flour, baking powder, bicarbonate of soda, cinnamon, ginger, nutmeg, and salt.
In a separate bowl, whisk the brown sugar, sunflower oil, and eggs until well combined. Stir in the grated carrots, vanilla extract, and any optional ingredients like raisins or walnuts.
Gradually fold the dry ingredients into the wet mixture using a spatula, being careful not to overmix.
Divide the batter evenly between the prepared cake tins. Bake for 25-30 minutes, or until a skewer inserted into the center comes out clean. Allow the cakes to cool in their tins for 10 minutes, then transfer them to a wire rack to cool completely.
Beat the cream cheese and butter together until smooth and creamy. Gradually add the icing sugar and beat until fully combined. Stir in the vanilla extract and orange zest, if using.
Place one cake layer on a serving plate and spread a generous amount of frosting on top. Place the second layer on top and spread the remaining frosting over the top and sides of the cake.
