Add the balsamic vinegar to a 2/3 cup measure and then fill with half and half.
Blend the Xylitol until it is a powder
Beat the coconut oil and butter for 5 minutes - until blended and fluffy.
Add the Xylitol and vanilla and beat until mixture is well blended.
Add in the eggs and egg yolk, one at a time, beating a few minutes after each one.
Blend the cocoa, coconut flour, almond flour, salt, Xanthan gum, and baking powder.
With the mixer on low add the flour mixture alternately with the cream mixture, beginning and ending with the flour.
Spoon into the prepared loaf pan.
Sprinkle with coconut and a tablespoon of Xylitol.
Bake at 325 for 50 - 60 minutes, or until cake tests done with a toothpick.
Let cool for 10 minutes in the pan and then cool completely on the counter before serving.
Serve with a dollop of whipped cream sweetened with your favorite sugar free sweetener and dusted with cocoa.
*Caution- some people are sensitive to Xylitol in large amounts and it can cause digestive upset in them. If you don't know how you respond to this sweetener eat only a small piece to make sure you handle it. You can substitute your favorite cup for cup measured sugar-free sweetener (sucralose, erythitol, etc.) for the Xylitol