Start by preheating your oven to 180°C (350°F). Meanwhile, prepare your cake tins by greasing them with unsalted butter and dusting with a bit of flour. This ensures that your cake won’t stick after baking, resulting in a beautiful presentation when you flip them over.
In a large bowl, whisk together the two eggs and the sunflower oil until well combined. Gradually add in the dark brown sugar and continue to whisk. The mixture should be smooth and slightly glossy, a sure sign you've created a solid base.
In another bowl, combine the gluten-free self-raising flour, ground ginger, ground cinnamon, and any optional spices you’re using, like nutmeg (which adds a lovely depth). Sift this mixture into the bowl with the wet mixture. Gently fold everything together until you can no longer see dry flour.
Now comes the fun part! Grate the apple and carrots, and fold them into the batter alongside the sultanas and walnuts (if you’re using them). The grated apple not only adds moisture but also a delightful sweetness to balance the spices.
Zest and juice the orange directly into the mixture. This adds a refreshing brightness that will really lift the flavors. If you’re feeling adventurous, a dash of vanilla extract can also enhance the aroma significantly.
Carefully pour the batter into your prepared cake tins, distributing evenly. Pop them in the oven and bake for about 25-30 minutes, or until the tops are golden and a skewer comes out clean when inserted into the center. Don’t be tempted to open the oven too early; the cake needs its time to rise and develop.
Once baked, remove the cakes from the oven and let them cool in their tins for about 10 minutes. Gently flip them onto a wire rack to cool completely. While the cakes cool, you can prepare the icing. Combine softened butter, cream cheese, powdered sugar, and the remaining orange zest in a bowl. Mix until smooth.
Once your cakes have cooled, spread a generous layer of icing on top of one layer. Place the second layer on top and ice the top. Finish by sprinkling chopped walnuts on top for a lovely presentation.