Add all ingredients to a small saucepan and place over medium-low heat.
Heat the mixture until it just starts to lightly simmer and the cocoa powder is completely absorbed, 10 to 15 minutes, whisking frequently to combine the ingredients. Monitor carefully to avoid overheating and burning the chocolate -- the mixture should be barely hot enough to simmer.
Turn off the heat. Stir to make sure all ingredients are well-combined, scraping up any chocolate stuck to the sides of the pan.
Pour the mixture into two mugs and serve.
Optional for a foamier drink: Pour the mixture into a blender and blend until frothy. Alternately, use an espresso machine’s frothing attachment.
Optional toppings: Top with whipped cream. Sprinkle cocoa powder on top.
This recipe yields 3 g net carbs per serving. Nutrition information assumes erythritol is used as the sweetener, which cannot be digested by the body.