Heat oven to 160°C. Mix brown sugar and almond powder together. Sprinkle the mixture into the base and sides of a 20 cm-deep round cake tin.
Using an electric mixer, whisk the eggs and sugar together until the mixture is pale and thick. Add lemon rind and carrots. Whisk until smooth. Set aside.
In a medium bowl, mix spinach, flour and baking powder together. Carefully fold into the egg mixture and add the butter. Mix until well blended.
Pour the mixture into the prepared baking tin, spread to level and bake for 50 minutes until a skewer comes out clean. Remove from the oven and leave to cool completely.
