Preheat the oven to 180C/375F degrees.
Grease and line an 8inch springform cake tin with parchment paper.
In a medium bowl, mix the erythritol and butter together until soft and blended.
Add the egg yolks and vanilla extract and stir thoroughly.
Add the coconut flour, almond milk, salt, baking powder, lemon juice and rind and beat until combined.
In another bowl, whisk the egg whites until stiff.
Gently fold the egg whites into the cake mixture.
Add the blueberries and gently stir, taking care not to overwork the cake mixture.
Spoon the mixture into the baking tin and smooth evenly.
Bake for 35-40 minutes until firm.
Allow to cool, then slice, eat and enjoy!