My personal favorite -- egg liqueur cake -- might be a bit labor-intensive as you decide to make the egg liqueur yourself (commercial versions made with sugar unfortunately), however since there isn't a lot egg liqueur in this, you might get away with the regular version..
Ingredients
80g butter
100g erythritol (or other low-carb sweetener)
5 eggs
100g high-cocoa-content chocolate
200g ground hazelnuts
½ package baking powder
2 tbsp egg liqueur in dough
Mix ingredients and bake at 180 degrees centigrade for half an hour to one hour (done when a tooth pick comes out clean)
2 cups of whipped cream (cover cake and place little rosettes around the edge of cake)
Egg liqueur to decorate (pour inside the rosettes and spread across the surface by tilting cake.
Egg liqueur is basically a mixture of eggs (egg whites and egg yolks whipped separately, add powdered erythritol and whiskey).