In a small saucepan, heat the half-and-half over medium-low heat until small bubbles appear around the edges. Don't allow it to come to a boil.
Lower the heat to low. Whisk in the stevia and the cocoa powder until fully incorporated.
Turn the heat off, leaving the saucepan on the hot burner. Stir in the chopped chocolate until melted.
If desired, garnish with a dollop of keto whipped cream and a dusting of cocoa powder, then serve.
It's best to use Dutch-processed cocoa powder in this recipe. This cocoa powder is treated with alkali, making it milder, darker, and less acidic than natural cocoa powder. It's not that the recipe won't work with natural cocoa powder. But it won't taste as good, in my opinion.