Add the chocolate and butter to a microwave-safe bowl and heat in 20 second intervals, stirring after each one, until melted and smooth. Allow to cool completely to room temperature.

In a separate bowl, whip together the egg whites and sugar until stiff peaks form.

Add the egg yolks to the chocolate mixture, and whisk until almost combined. Do not fully whisk them into the chocolate.

Fold in the whipped egg whites, then gently fold in the whipped cream until incorporated and no more white streaks remain.

If the mixture becomes grainy from the chocolate, simply microwave in 10 second intervals, gently folding after each one, until the mixture becomes more smooth.

Divide the mixture between 3 - 4 small glasses or ramekins, and refrigerate for at least 3 - 4 hours.

Before serving, garnish with extra whipped cream and chocolate shavings.