Preheat the oven to 180/160 fan. Line the baking tin.
Add the eggs, sugar and citrus zest into a bowl. Whisk until pale and fluffy. You want to aim for about three times the original volume. Slowly drizzle in the oil whilst still whisking.
Add the dry ingredients and fold through until combined. Then add the carrot and the walnuts.
Pour into the tin and bake for 40 mins or until a wooden skewer inserted comes out with a few crumbs, but cleanly. Let it cool.
Mix all of the frosting ingredients in a bowl.
Once the cake has cooled, top with the frosting and nuts. Slice and enjoy.
