Preheat oven to 180°C conventional oven
Mix together plain flour, baking powder, baking soda, cinnamon, mixed spice, and salt
Combine white sugar and soft dark brown sugar
Beat eggs and mix with vegetable oil and vanilla extract
Combine wet and dry ingredients
Fold in freshly grated carrot and chopped walnuts
Pour batter into a 22.5cm x 27.5cm pan
Bake for approximately 35 minutes or until firm to the touch
Allow cake to cool completely
Cream butter and icing sugar together for about 2 minutes
Add cream cheese, vanilla extract, and fresh lemon juice to the butter mixture
Whisk until smooth and creamy
Chill frosting for 20-30 minutes
Top cooled cake with lemon cream cheese frosting, chopped walnuts, and orange zest
