Beat the base smooth. In a medium bowl, beat the softened cream cheese with a hand mixer on medium speed until completely smooth, about 1 minute. Scrape the bowl — any lump left now stays lumpy forever.
Add the dry ingredients. Beat in the powdered erythritol, cocoa powder, vanilla, and salt until you have a thick, even paste, about 30 seconds. (Powdered sweetener is non-negotiable here; granulated stays gritty.)
Whip the cream separately. In a second cold bowl, whip the heavy cream to firm peaks — when you lift the beaters, the peaks stand straight up.
Fold, don't stir. Add one-third of the whipped cream to the chocolate base and stir to loosen it. Then fold in the remaining cream in two additions with a spatula, cutting down the middle and turning the bowl, until no streaks remain.
Chill. Divide among 4 small glasses or ramekins, cover, and refrigerate at least 1 hour (2 is better). Top with dark chocolate shavings before serving.