Preheat your oven to 325 degrees F and line an 8x8-inch baking pan with parchment paper, leaving an overhang on two sides for easy removal. In a bowl, mix the almond flour, melted butter, and 2 tablespoons erythritol until it resembles wet sand.
Press the crust mixture firmly and evenly into the bottom of the prepared pan. Bake for 10 to 12 minutes until the edges are just starting to turn golden. Remove and let it sit while you prepare the filling.
In a small bowl, mash the fresh raspberries with 1 tablespoon erythritol using a fork until you have a thick, chunky puree. Set aside.
In a large bowl, beat the softened cream cheese and 1/2 cup erythritol with an electric mixer on medium speed until completely smooth, about 2 minutes. Add the eggs one at a time, mixing on low after each until just combined.
Add the vanilla extract and sour cream, and mix on low speed until the batter is silky and uniform. Do not over-beat or the bars may crack.
Pour the cheesecake batter over the pre-baked crust and smooth the top with a spatula. Drop spoonfuls of the raspberry puree across the surface of the batter.
Use a toothpick or the tip of a thin skewer to drag through the raspberry dots in a swirling pattern, creating a beautiful marbled effect. Be gentle so you do not disturb the crust below.
Bake for 30 to 35 minutes, until the edges are set and the center has just a slight jiggle. Turn off the oven, crack the door open, and let the bars cool inside for 15 minutes before moving them to the counter. Refrigerate for at least 3 hours or overnight before lifting out and slicing into bars.
