Preheat oven to 350°F (175°C). Pulse almond flour, ⅓ cup erythritol, and butter in a food processor until crumbly. Press mixture into a 9-inch springform pan.
In a bowl, beat cream cheese, ¾ cup erythritol, and vanilla until smooth. Whisk in eggs one at a time, then fold in heavy cream. Pour half the batter over the crust.
In a separate bowl, whisk cocoa powder into remaining batter until smooth. Spoon it into a zip-top bag with a corner snipped off. Pipe alternating strips over the vanilla layer. Microwave 15 seconds to soften, then swirl with a toothpick.
Bake 45 minutes until center is just set. Cool, then refrigerate 6 hours before slicing.