Preheat the oven to 180C/375F degrees.

Grease and line an 8 inch springform cake tin with parchment paper.

In a 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, salt, baking powder and beat until combined.

In another bowl, whisk the egg whites until stiff.

Gently fold the egg whites into the cake mixture.

Spoon the mixture into the baking tin and smooth evenly.

In a bowl, add the softened cream cheese and beat with the erythritol (or sugar substitute).

Add the egg, vanilla extract, lemon juice, zest and beat until smooth.

Spoon this mixture over the cake mixture into the cake tin and smooth evenly.

Scatter the blueberries over the cream cheese mixture.

For the topping, place the coconut flour, cinnamon and erythritol in a bowl and mix until combined.

Add the butter and mix with your hands, gently, so that the mixture looks like breadcrumbs.

Scatter the topping over the blueberries.

Bake for 40-45 minutes until firm and the top is cooked.

Remove from the oven, allow to cool, then place in the fridge to firm.