Preheat the oven to 350°F (175°C) and line the bottom of a 9-inch springform pan with parchment paper.
In a mixing bowl, combine almond flour, melted butter, erythritol, and vanilla extract until a dough forms.
Press the dough into the bottom of the prepared pan, forming an even layer.
Bake for 10 minutes, then remove from oven and set aside to cool.
In a large bowl, beat the softened cream cheese and erythritol with an electric mixer until smooth.
Add eggs one at a time, mixing well after each addition.
Blend in sour cream, lemon juice, and vanilla extract until the mixture is uniform and creamy.
Pour the cheesecake mixture over the cooled crust, smoothing the top with a spatula.
Bake for 45-50 minutes or until the edges are set and the center is slightly jiggly.
Turn off the oven, crack the door open and allow the cheesecake to cool inside for 1 hour to prevent cracking.
Remove cheesecake from the oven and cool to room temperature, then refrigerate for at least 4 hours or overnight.
In a medium saucepan, whisk together heavy cream, egg yolks, erythritol, and vanilla extract over medium heat.
Cook, continually whisking, until the mixture thickens and coats the back of a spoon.
Sprinkle xanthan gum over the custard, whisking vigorously to prevent clumps.
Remove from heat and let the custard cool to room temperature, then spread evenly over the chilled cheesecake.
Refrigerate to set while preparing the ganache.
Heat the heavy cream in a saucepan until it just begins to simmer.
Remove from heat and add the chopped chocolate and butter, letting them sit for a minute to melt.
Stir until smooth and glossy.
Pour the ganache over the custard layer, spreading to cover completely.
Refrigerate the cheesecake for at least 2 hours or until the ganache is set.
Once set, run a knife around the edges of the cheesecake and release it from the springform pan.
Slice and serve chilled.