Preheat oven to 160°C (320°F).
Mix almond flour, butter, erythritol, and vanilla until crumbly.
Press mixture into a lined baking pan to form crust.
Bake crust for 10 minutes, then let it cool.
Beat cream cheese until smooth and creamy.
Add heavy cream, sweetener, and vanilla; mix well.
Add eggs one at a time and mix gently.
Pour half the filling over crust.
Swirl in blackberry puree, then add remaining filling.
Gently swirl again for a marbled effect.
Bake for 45–50 minutes until center is slightly set.
Turn off oven and let cheesecake cool inside with door slightly open.
Refrigerate for at least 4 hours before serving.