Crust: Mix together 1 ½ cups almond flour, 3 tablespoons melted butter, 1 tablespoon erythritol and a pinch of salt. Press into a 9-inch pie pan and bake at 180°C for 10–12 minutes or until golden. Let it cool completely.
Toffee Layer: Melt ½ cup butter in a saucepan, add ½ cup erythritol and cook until lightly caramelized. Whisk in ½ cup heavy cream and ½ tsp of vanilla extract until thick and smooth. Allow it to cool slightly.
Cream: Beat 1 cup heavy cream with 1 tbsp powdered erythritol and ½ tsp banana extract until soft peaks form.
Put the cake together: Pour the now-cooled toffee over the base, pipe or spread a layer of whipped cream over it, refrigerate for 2 hours and sprinkle with chocolate shavings (or dust with cocoa) before serving.