Prep the pan and oven. Heat the oven to 325°F (165°C). Line an 8-inch square baking pan with parchment, leaving overhang on two sides for easy lifting. Lightly grease the exposed sides.

Make the almond crust. In a bowl, whisk almond flour, granulated sweetener, salt, and cinnamon. Stir in melted butter and vanilla until the mixture looks like damp sand and clumps when pressed.

Press and par-bake. Press the crust evenly into the pan. Dock with a fork a few times. Bake for 10–12 minutes until lightly set and just turning golden at the edges. Cool 5 minutes.

Blend the filling. With a hand mixer, beat cream cheese and powdered sweetener on medium until smooth and fluffy, 1–2 minutes. Add eggs one at a time, mixing on low just to combine. Mix in sour cream, vanilla, almond extract, and salt. Do not overbeat.

Make the quick blueberry mixture. In a small saucepan, add blueberries, lemon juice, powdered sweetener, and zest. Warm over medium heat for 2–4 minutes, stirring, until some berries burst and you have a spoonable mixture. Let it cool slightly.

Assemble. Pour cheesecake filling over the warm crust and smooth the top. Dollop blueberry mixture in small spoonfuls over the surface. Use a skewer or knife to gently swirl. Sprinkle sliced almonds over the top if using.

Bake. Bake 22–28 minutes, until the edges are set and the center wobbles slightly when you jiggle the pan. Avoid overbaking; carryover heat will finish the job.

Cool and chill. Cool on a rack for 1 hour. Refrigerate at least 3 hours, preferably overnight, until fully set.

Slice and serve. Use the parchment overhang to lift the slab out. Warm a sharp knife under hot water, wipe dry, and cut into 12–16 bars. Serve as is or with a few extra fresh blueberries on top.