Preheat the oven to 350°F (175°C). Butter a 9-inch (22 cm) springform and line the base with parchment paper.
Melt the butter for the crust and heat until it gets a nutty scent. This will give the crust a lovely toffee flavor.
Remove from heat and add almond flour, sweetener and vanilla. Combine into a dough and press into the base of the springform pan. Bake for 8 minutes, until the crust turns lightly golden. Set aside and allow to cool while you prepare the filling.
Mix together cream cheese, heavy cream, eggs, lemon zest, vanilla and sweetener, if you’re using any. Combine well. Pour the mixture over the crust.
Raise the heat to 400°F (200°C) and bake for 15 minutes.
Lower the heat to 230°F (110°C) and bake for another 45-60 minutes.
Turn off the heat and let cool in the oven. Remove when it has cooled completely and place it in the fridge to rest overnight. Serve with fresh blueberries.