Preheat the oven to 170°C (fan 150°C, gas mark 3) and grease an 28cm (11in) springform cake tin.
Cream 180g of the sugar, zests and egg yolks together until light and fluffy. Next, stir in the ground almonds, almond extract and the cinnamon.
In a separate bowl, beat the eggs whites with the remaining sugar until stiff. Add about one-quarter of the egg whites into the thick almond mixture and beat. Add a further quarter and repeat. Add the remaining egg white mixture and fold in until fully combined.
Turn the mixture into the prepared tin and bake in a preheated oven for 40 minutes.
Remove from the oven, allow to cool for 10 minutes in the tin and then turn out onto a wire rack.
To follow the time-honoured tradition of decoration, find the shape of the St James cross using the internet and print it out. Cut out the middle of the cross to use as a stencil.
Once the cake is cooled, dust the cake with icing sugar and serve straightaway