Line the pan: Line an 8x8-inch pan with parchment, leaving overhang on two sides for easy lifting later. This helps the cake come out cleanly for neat slices.

Whip the cream: In a large chilled bowl, beat the cold heavy cream until soft peaks form. Don’t overmix yet.

Make the mascarpone mixture: In a separate bowl, whisk mascarpone with powdered sweetener, cocoa powder, vanilla, espresso powder (if using), and a pinch of salt until smooth and creamy.

Fold together: Add one-third of the whipped cream to the mascarpone mixture and whisk gently to lighten. Then fold in the remaining whipped cream with a spatula until fully combined and fluffy. Taste and adjust sweetness if needed.

First layer: Spread a thin layer of the chocolate cream on the bottom of the pan to anchor the cookies.

Add cookie layer: Arrange a tight, even layer of low-carb chocolate wafers over the cream, breaking a few to fill gaps. Aim for full coverage.

Repeat layers: Spread about one-third of the remaining cream over the cookies. Repeat with another cookie layer, then cream, ending with a final layer of cream on top. You’ll have 2–3 layers of cookies depending on thickness.

Top and chill: Smooth the top, then sprinkle on shaved dark chocolate or cocoa nibs. Cover the pan and refrigerate for at least 6 hours, ideally overnight. The longer it chills, the softer and more cake-like it becomes.

Slice and serve: Lift the cake out using the parchment overhang. Warm a knife under hot water, wipe dry, and slice into squares. Serve chilled.

Optional flourish: Add a dollop of lightly sweetened whipped cream or a few raspberries for contrast.