In a large bowl, beat heavy cream, vanilla beans, and salt with a whisk until stiff peaks form. Place bowl in refrigerator to chill before moving on.
Set up a bain marie by filling a small sauce pot with 2 cups of water place a metal bowl that will fit the pot but won't touch the water on top. Place pot over medium-low heat. Water should never go past a gentle simmer. Melt bittersweet chocolate in bowl. Once fully melted and smooth remove from heat and allow to cool. *(Be careful not to get any liquid in the chocolate or it will seize up).
In another bowl or stand mixer (preferred) whisk egg whites until soft peaks form. Continue to whisk as you add sugar in a slow stream until incorporated, add vinegar and continue whisking until stiff peaks form.
Pour melted but cooled chocolate into egg whites and fold gently to incorporate. Once chocolate is incorporated in egg whites add whipped cream and fold again. Pour in serving cups and refrigerate until ready to serve. Garnish with shaved white or dark chocolate if desired.
