Grease your favourite serving dish with butter then line with parchment paper.
Mix all the ingredients for the cookie crust in a small mixing bowl then press firmly into the lined serving dish. The firmer you press, the stronger the cookie crust will hold together when serving. Place it in the fridge while you make the next layer.
Vanilla cheesecake layer
Place all the vanilla cheesecake ingredients in the food processor and blend until smooth. Taste and adjust if you need more sweeteener.
Gently spread the cheesecake layer on top of the cooled cookie crust. Place back in the fridge to set.
Chocolate custard layer
In a medium saucepan, gently mix the butter, cream, sweetener, cocoa, and vanilla together. Warm slowly until the cream mixture is hot, but NOT boiling or bubbling.
In a heatproof jug, whisk the egg yolks and add ¼ cup of warm cream mixture. Slowly add this yolk/cream mixture back into the saucepan with the rest of the warm cream mixture. Continue to heat and mix until the chocolate custard thickens.
Once the chocolate custard has thickened, remove it from the heat and allow it to cool for a few minutes. Sprinkle the xanthan gum over the surface and whisk vigorously until the custard is thick and continue to whisk until almost cool and set.
Pour the custard over the cooled cheesecake layer. Place back in the fridge to continue setting.
Whip all the cream topping ingredients together until light and fluffy. Spread gently over the chocolate custard layer.
Place the finished dessert back in the fridge to set, for at least 2 hours, but the layered lasagna tastes even better if left covered in the fridge overnight.
Decorate and serve
When it's time to serve your chocolate lasagna, sprinkle the top with cocoa powder or drizzle with melted sugar-free chocolate.