Get your stand mixer out with the whisk attachment, and chill the mixing bowl in the fridge while you make your mousse base.

In a large pot, create a double broiler with another bowl on top. On medium-low heat, whisk your egg yolk and sugar. Once it gets custardy, and doubles in size, add in your chocolate, and melt until smooth, about 12 to 15 minutes.

Add a dash of cream and salt and stir until incorporated. Set aside off the heat.

Remove your bowl from the fridge, and add your heavy whipped cream, sugar, and vanilla extract. We use a stand mixer on the highest setting until fully whipped, about 10 to 12 minutes. You can do this with your hand, just keep whisking until it's completely whisked, it will take longer this way. Reserve about 1/4 cup whipped cream for topping and transfer to the fridge.

For the remaining whipped cream, slowly and gently fold in the melted chocolate in the whipped cream, scraping the sides and folding over slowly, and not over-mixing. You can mix gently in an 8 formation until incorporated. Do this until the whipped cream and melted chocolate is blended together with no streaks from the whipped cream. Pour evenly into 4 small to medium cups or ramekins. Chill in the fridge for at least 4 hours, and up to overnight.

When ready to serve, top each cup with your remaining whipped cream and chocolate shavings from your reserved chocolate (we just use a peeler to shave them on top).