Roast Nuts: Preheat the oven to 140°C (285°F) fan-assisted or 160°C (320°F) conventional. Place nuts on a baking tray in a single layer and roast for about 25 minutes until golden and fragrant. (Optional: Can use raw nuts)

Prepare Base: Process warm nuts in a food processor until finely chopped. Add sweetener, butter, and vanilla, and process again until it comes together. Press this mixture into a springform pan lined with parchment paper and refrigerate.

Cheesecake Layer: In a bowl, mix 2 cups of heavy cream with cream cheese (or mascarpone), sweetener, lemon juice, and zest until smooth and creamy using a mixer. Spread over the chilled nut base and refrigerate for at least 3 hours.

Final Touches: Beat the remaining heavy cream to stiff peaks and pipe or spread over the cheesecake. Decorate with lemon slices.

To Serve: Run a sharp knife around the edges to release the cheesecake. Serve immediately or chill for an hour. Store in the fridge for up to 5 days.