Melt the chocolate and 2 tbsp (30g) of heavy cream in a double boiler or a microwave in a microwave-proof bowl. Stir the chocolate to make sure it is evenly melted. Once melted, place the chocolate in the refrigerator for 15 minutes to cool down.
In the meantime, combine a heavy cream, and protein powder, and optionally powdered sweetener into the mixing dish. Use a hand mixer or a standing mixer to beat the cream until firm peaks form.
Remove the cooled chocolate from the refrigerator. Using a rubber spatula, gently fold in whipped cream into the chocolate until combined. Portion the mixture into serving cups and refrigerate for at least 3 hours to let the mousse firm up before serving.
Serve with more whipped cream sprinkled with chocolate shavings.