Preheat the oven to 175C fan forced and grease and line a 9inch cake tin with baking paper.
Beat the egg yolks and maple syrup together until thick, creamy and light in colour.
Fold in the almond flour and lemon zest.
In another bowl beat the egg whites until soft peaks then gently mix in the cream of tartar. Gently fold the egg white mixture into the cake batter one spoonful at a time being very careful not to knock out too much of the air.
Gently poor into the prepared cake tin and bake in the preheated oven for 25-30 minutes. Until a skewer inserted into the centre comes out clean.