Prep the pan: Line an 8x8-inch square pan with parchment, leaving overhang on two sides for easy lifting.
Preheat oven to 325°F (163°C).
Make the cookie crumble: In a bowl, whisk almond flour, cocoa, sweetener, and salt. Stir in melted butter and vanilla until it looks like damp sand. It should clump when pressed.
Reserve some for topping: Scoop out about 1/3 cup of the crumble and set aside for the finishing layer.
Form the base: Press the remaining crumble firmly and evenly into the lined pan.
Use the bottom of a measuring cup to compact it well. Bake for 8–10 minutes, just until set. Let it cool slightly while you make the filling.
Beat the filling: In a mixing bowl, beat cream cheese until smooth, about 1 minute.
Add sweetener, sour cream, vanilla, and salt; beat until creamy. Add egg and mix on low just until combined. Do not overbeat.
Layer and bake: Pour the filling over the baked base and smooth the top.
Bake at 325°F for 18–22 minutes, until the edges are set and the center has a slight jiggle.
Cool completely: Let the pan cool on a rack until room temperature. Then refrigerate for at least 3 hours, preferably overnight, until fully set.
Make the whipped topping: Whip heavy cream with vanilla (and sweetener if using) to soft peaks. Fold in half of the reserved crumble to create a cookies-and-cream look.
Finish the top: Spread the whipped mixture over the chilled cheesecake.
Sprinkle the remaining crumble on top for texture.
Slice into bites: Lift the slab out using the parchment overhang. Use a sharp knife wiped clean between cuts to slice into small squares or bars.