Preheat the oven to 350°F (175°C) and grease a 10-inch springform pan. In a medium bowl, whisk together the baking mix, oat fiber, sweetener blend, xanthan gum, and salt. Add the softened salted butter and Greek yogurt. Mix with a hand mixer until the mixture forms coarse crumbs. Press this crust mixture evenly into the bottom of the greased springform pan. Bake for 6 minutes, then remove from the oven. Lower the oven temperature to 325°F (163°C).

In a blender, combine the black raspberries, water, xanthan gum, and a dash of salt, then blend until smooth. Pour the mixture into a saucepan and bring to a boil over medium heat. Reduce heat and let simmer for 5 minutes. While it simmers, stir in the sweetener blend to your desired level of sweetness. Once simmered, strain the raspberry mixture through a fine sieve with the back of a spoon to remove the seeds, leaving you with about 1 cup of thick raspberry syrup. Set the syrup aside to cool completely before assembling the cheesecake. I like to taste the raspberry syrup and adjust the sweetness to ensure a bright berry flavor.

In the bowl of a stand mixer, beat the room-temperature reduced-fat cream cheese until completely smooth and creamy. Add the full-fat sour cream, eggs, gentle sweetener, additional sweetener blend, cream of tartar, and vanilla extract. Beat the mixture for about 2 minutes, scraping down the sides as necessary, until everything is well combined and smooth.

Pour the cheesecake filling (from Step 3) over the pre-baked crust (from Step 1) in the springform pan. Dollop the cooled raspberry syrup (from Step 2) in several separate blobs on top of the cheesecake filling. Using a knife, gently swirl the raspberry blobs into the cheesecake mixture to create an attractive marbled pattern.

Wrap the sides of the springform pan with a wide piece of aluminum foil to help prevent any water from leaking into your cheesecake. Place the wrapped pan into a larger baking dish and pour hot water into the larger pan until it reaches about 3/4 inch up the sides of the springform pan, creating a water bath. Bake at 325°F (163°C) for 1 hour. The center should still jiggle slightly for a creamy texture. If you prefer a firmer cheesecake, bake a little longer. After baking, turn off the oven and leave the cheesecake inside with the door slightly open for about 10 minutes so it can cool slowly; I find this helps prevent cracks on the top.

Remove the cheesecake from the water bath and unwrap the foil. Let it cool at room temperature to finish settling, then refrigerate overnight or until thoroughly chilled. This ensures the cheesecake slices beautifully and all the flavors meld together.