Prep the pan and oven: Preheat your oven to 325°F (163°C). Line an 8x8-inch pan with parchment, leaving a little overhang so you can lift the bars out later. Lightly grease the sides.

Make the crust: In a bowl, mix almond flour, granulated sweetener, and salt. Stir in melted butter and vanilla until it looks like damp sand. Press the mixture firmly into the pan in an even layer.

Par-bake the crust: Bake for 10–12 minutes, until the edges are just starting to color. Set aside to cool slightly while you make the filling. Keep the oven at 325°F.

Cook the blackberry swirl: In a small saucepan, combine blackberries, powdered sweetener, lemon juice, and zest. Cook over medium heat for 5–7 minutes, stirring and smashing berries, until juicy and slightly thickened. Taste and adjust sweetness. Strain through a mesh sieve to remove seeds, if you like, and let it cool to lukewarm.

Beat the filling: In a mixing bowl, beat the softened cream cheese and powdered sweetener on medium speed until smooth and fluffy, about 1–2 minutes. Add eggs one at a time, mixing just until combined. Mix in vanilla, sour cream, and a pinch of salt. Do not overbeat.

Assemble: Pour the cheesecake filling over the warm crust and smooth the top. Spoon the blackberry sauce in small pools over the surface. Use a toothpick or knife to gently swirl. Don’t overdo it—4–6 swirls are enough.

Bake: Bake for 22–28 minutes, until the edges are set and the center has a slight wobble. The top should look matte, not wet.

Cool and chill: Let the pan cool on a rack for 1 hour. Then refrigerate, uncovered, for at least 3 hours (overnight is best). This helps the bars set and slice cleanly.

Slice and serve: Lift the slab out with the parchment. Use a sharp knife, wiped clean between cuts, to slice into 12–16 bars. Serve chilled.