Preheat the oven to 160˚C and grease an 20cm cake tin.
In a bowl, pour 180g of caster sugar, orange and lemon zests and beat with the egg yolks until light and fluffy.
Next, stir in the ground almonds, almond extract and the ground cinnamon.
In a separate bowl, beat the egg whites with the remaining 75g of caster sugar until stiff. Pour a quarter of the meringue into the egg yolk and almond mixture and gently fold. Repeat until all the meringue is folded into the almond mixture.
Pour the mix into the prepared tin and bake for 35-40 minutes until cooked through.
Remove from the oven, allow to cool for 10 minutes in the tin and then turn out onto a wire rack.
When cooled dust with icing sugar using a pattern of the St James cross if desired.
Enjoy within a few days!