Adjust the oven rack to the middle position, pre-heat the oven to 350ºF (180ºC) and line a 9-inch (23cm) square baking tin with parchment/baking paper.
Tip: When lining the baking tin, I recommend leaving some parchment/baking paper overhang, as that will help with removing the cake from the tin later on.
In a large bowl, whisk together the light brown sugar, oil, eggs and vanilla until well combined.
Sift in the gluten free flour blend, baking powder, baking soda, xanthan gum, salt, cinnamon, ginger and nutmeg.
Whisk everything together into a smooth batter with no flour clumps.
Add the coarsely grated carrots and roughly chopped walnuts, and fold them into the batter until they're evenly distributed throughout.
Transfer the batter into the lined baking tin and smooth out the top.
Bake at 350ºF (180ºC) for about 35 minutes or until well risen, golden-brown on top and an inserted toothpick/cake tester comes out clean. If the cake starts browning too quickly, cover it with a sheet of aluminium foil (shiny side up) and continue baking until done.
Allow the cake to cool in the baking tin for about 10-15 minutes, then transfer it out of the tin onto a wire rack to cool completely.
Tip: It’s important that your cake is cooled completely before you spread the cream cheese frosting on top.
Cream cheese frosting:
You can make the cream cheese frosting with a stand mixer fitted with the whisk attachment, with a hand mixer fitted with the double beaters, or by hand using a large balloon whisk.
In a large bowl (or the bowl of a stand mixer, if using), whisk the cream cheese until it's smooth and looser in texture.
Add the heavy/double cream, powdered/icing sugar and vanilla, and whisk until soft peaks form. The frosting should keep its shape when you swirl it around with a spoon or a rubber spatula – you don't want it too loose or runny, but be careful not to over-whip it as that can make it too stiff and too thick.
Spread the cream cheese frosting on top of the cooled carrot cake all the way to the edges, using a small offset spatula or the back of a spoon to add some decorative swirls and swoops.
Sprinkle on some extra chopped walnuts as decoration, slice and serve.