Preheat the oven to 350F.

To make the cake, mix together the egg yolk, melted butter, heavy cream, baking powder and sweetener. Stir in the almond flour to make a thick paste.

Whisk the egg white until soft peaks form, then fold it carefully into the almond mixture.

Spoon the mixture into individual pudding cups. Place on a baking tray and bake for 10-12 minutes or until the center is cooked. Let cool for 5 minutes, then turn out onto a cooling rack.

For the sauce, add the butter, sweetener, and water to a small saucepan. Bring to a boil and keep cooking for 5 minutes - but don't let it burn! Add a pinch of thickener (if using) and whisk until thickened.

Place the almond cakes onto serving plates, then pour the warm sauce over the top.