Preheat the oven to 350°F and line a 10x15 inch baking sheet with parchment paper. Whisk the almond flour, cocoa powder, granulated allulose, baking powder and salt in a bowl.
Add the eggs, melted butter and vanilla extract and stir into a thick, smooth batter. Spread it evenly across the baking sheet in a thin layer.
Bake for 10 to 12 minutes, just until set but still soft. Let it cool completely, then slice it in half crosswise into two equal rectangles and freeze both pieces for 20 minutes.
Beat the cream cheese, powdered allulose, vanilla extract and salt with 1/4 cup of the heavy cream until smooth. Whip the remaining cream to stiff peaks and fold it in.
Place one cookie rectangle on a lined tray, spread the vanilla filling over it in an even layer, then top with the second rectangle and press down gently.
Cover and freeze for at least 6 hours, until the filling is completely firm.
Trim the edges for clean sides and slice into 12 sandwiches. Wrap each one individually in parchment and keep frozen until serving.