In a large mixing bowl, whip the heavy cream, granulated sugar, and vanilla extract together until soft peaks form. Be careful not to overwhip.
In another bowl, beat the egg whites and salt until stiff peaks form.
Gently fold the whipped cream into the egg whites in three additions, being careful to maintain the light and airy texture.
Once fully combined, spoon the mousse into individual serving dishes or a large bowl.
Cover and refrigerate for at least 2 hours, or until set.
Before serving, dust with powdered sugar if desired.