In a small saucepan over low heat, combine the raspberries and water. Bring to a simmer andn then cook until the raspberries can be easily mashed.
Stir in the sweetener to taste, then whisk in the glucomannan to thicken it. Let cool completely.
Preheat the oven to 325F and lightly grease a 9×9 inch square pan.
In a medium bowl, whisk together the almond flour, cocoa powder, sweetener, and salt. Stir in the butter until well combined.
Press firmly into the bottom of the prepared baking pan and bake 12 minutes. Let cool while preparing the filling.
Reduce the oven temperature to 300F.
In a small heatproof bowl set over a pan of barely simmering water, melt the white chocolate with the cocoa butter, stirring until smooth. Do not walk away, as white chocolate can seize very easily. Remove the bowl from over the heat once melted.
In a large bowl, beat the cream cheese with the sour cream until smooth. Beat in the sweetener until well combined, then beat in the melted white chocolate. Add the egg and vanilla extract and beat until just combined.
Dollop about half of the cheesecake mixture over the crust and then drizzle half the raspberry sauce over top. Repeat with remaining cheesecake mixture and remaining sauce.
Use a knife or a skewer to swirl together. Gently shake the pan to even out the filling.
Bake 30 to 35 minutes, until the edges of the cheesecake are set but the center still jiggles slightly. Remove and let cool completely, then refrigerate 3 hours before cutting.