Place the chopped chocolate and butter in a heat-safe bowl. Melt gently over a double boiler or in short microwave intervals, stirring until smooth. Set aside to cool slightly.

In a large mixing bowl, whip 1½ cups of the heavy cream until soft peaks begin to form. Avoid overwhipping.

Stir the vanilla extract and salt into the melted chocolate mixture until combined.

Gently fold the whipped cream into the chocolate mixture in several additions. Use a spatula and fold carefully to maintain as much air as possible.

Divide the mousse evenly among serving glasses or dessert dishes.

Refrigerate for at least 2 hours, or until the mousse is chilled and set.

Whip the remaining ½ cup heavy cream with the powdered sugar until medium peaks form.

Top each serving with sweetened whipped cream before serving. Garnish with chocolate shavings, cocoa powder, or fresh berries if desired.

Serve chilled and enjoy.