Chop dark and milk chocolate into small pieces
Melt chocolate using a double boiler or microwave in short intervals
Stir until smooth and let cool slightly
In a separate bowl, whip heavy cream and sugar until soft peaks form
Add vanilla extract, cocoa powder, and salt to the melted chocolate
Fold a portion of whipped cream into chocolate to lighten the mixture
Gently fold in remaining whipped cream until smooth and airy
Spoon mousse into serving cups or bowls
Chill in the refrigerator for at least 1–2 hours until set
Top with chocolate chips or whipped cream before serving