Preheat your oven to 350°F (175°C). Line an 8x8 inch baking pan with parchment paper, leaving some overhang for easy removal.
Make the crust: In a mixing bowl, combine almond flour, erythritol, melted butter, and vanilla extract until a dough forms. Press the mixture into the bottom of the prepared pan, creating an even layer. Bake for 10 minutes, then remove and set aside to cool slightly.
Prepare the cheesecake mixture: In a large bowl, beat the softened cream cheese and erythritol together until smooth. Add the eggs one at a time, fully incorporating each before adding the next. Stir in the vanilla extract and sour cream until the mixture is completely smooth.
Assemble the bars: Pour the cheesecake mixture over the cooled crust and spread out evenly.
Make the raspberry swirl: In a small saucepan over medium heat, combine the raspberries, erythritol, and lemon juice. Cook until the raspberries break down and the mixture slightly thickens, about 5 minutes. Pass the mixture through a fine-mesh sieve to remove the seeds, and dollop the raspberry sauce over the cheesecake layer.
Create the swirl effect: Use a toothpick or knife to swirl the raspberry sauce into the cheesecake layer, creating a marbled effect.
Bake: Place the pan in the oven and bake for 35-40 minutes, or until the cheesecake is set but still slightly jiggly in the center.
Cool and chill: Remove the cheesecake from the oven and let it cool to room temperature. Then refrigerate for at least 2 hours, or until fully set.
Serve: Lift the chilled cheesecake out of the pan using the parchment paper overhang, cut into bars, and serve.