Preheat oven to 350 degrees F (175 C) and grease a 9-inch springform pan.
For the carrot cake: In a large bowl, blend together the melted butter, erythritol, liquid Stevia, eggs, vanilla extract, and shredded carrot.
Add in the almond flour, coconut flour, ground cinnamon, baking soda, and a pinch of salt. Mix until just combined. Pour into the prepared pan.
For the cheesecake layer: In a large bowl, beat the cream cheese, erythritol, and liquid Stevia together until smooth. Mix in the eggs, vanilla extract, and lemon juice until just combined. Pour batter on top of the carrot cake layer.
Bake for 40-50 minutes or until the middle is mostly set with a slight jiggle. Cover with foil if the cheesecake is browning too much. Let cheesecake cool completely to room temperature, then refrigerate for at least 4 hours or overnight.
For the frosting: Beat the cream cheese, butter, powdered Swerve, vanilla extract, and heavy cream until smooth and fluffy. Frost the top of the cooled cheesecake and garnish with chopped nuts if desired.