Preheat the oven to 350 degrees.

To a sauce pan, add the erythritol, salt, and cocoa powder. Whisk to remove any lumps.

Add the half n half and egg yolks and whisk to combine.

Turn the heat to MED and add the butter. Whisk constantly until the mixture begins a LOW boil. This will take 15-20 minutes. Do not leave the the filling unattended or it will scorch. 

When the mixture begins to bubble, add the xanthan gum 1/4 tsp at a time whisking after each time. Let the mixture bubble and thicken as you keep whisking. It should become like a very thick pudding. Do not overcook.

Remove the pan from the heat and add the vanilla. Pour the filling into your pie shell.

To prepare the meringue, add the egg whites to the bowl of a mixer. With the mixer on high, beat the egg whites with the cream of tartar and vanilla extract until they become slightly firm. 

With the mixer still on high, add the last 1/4 cup of erythritol, a little a time. The meringue is done when it is firm and you can use the whisk to make peaks. It should hold its shape when done.

Pour the meringue on top of the hot pie filling. Be sure to seal the edges of the pie with the meringue to prevent shaping. Use a knife or spatula to make peaks in the meringue.

Bake the pie 5-10 minutes or until the meringue is golden brown and set.

Let the pie cool completely before serving. Store on the counter or refrigerator up to 1 week.