Preheat the oven to 250° F. Line a large rimmed baking sheet with parchment paper.
In double boiler over medium heat, melt chocolate. Remove from heat. Transfer from hot pan to a new, small bowl. Allow to slightly cool while you prepare the meringue (this will harden after a few minutes, so work quickly and keep a watchful eye).
In an electric mixer bowl, beat egg whites with vinegar on low speed until foamy.
Increase the speed to medium and slowly pour in vanilla powder and then sugar, as little as 1 tablespoon at a time. Beat until the whites are stiff and glossy. Add the espresso powder and continue to whisk in, but just until incorporated.
Remove bowl from mixer. Pour in half to 2/3rds of the room temp, melted chocolate. Using spatula, fold in meringue 2-3 times only. Keep the swirls for a stunning look.
Spoon meringue onto prepared baking sheet. Shape however you like, in whichever size you prefer. Just make sure that all meringues on your pan resemble the same size to ensure even cooking.
Bake for about 1 hour, or until the meringues are firm on the outside but still chewy in the
center. Let cool completely.
Reheat remaining ⅓ chocolate, drizzle before serving. Enjoy!