Heat the chocolate in a microwave-safe bowl for 30 seconds, then stir. If it’s not melted completely, nuke it for another 15 seconds. Allow to cool slightly while you make your meringue.
Preheat oven to 275°F. Line a large cookie sheet with parchment paper.
In a standing mixer fitted with the whisk attachment, whip the egg whites on high speed until light and foamy. Slowly add in sugar, cream of tartar, and salt, and continue to whip until stiff peaks form and the sugar granules absorb completely.
Remove meringue from mixer, and spoon melted chocolate on top of the meringue. Do not mix (it will naturally swirl as you spoon it!).
Use 2 large spoons to scoop the meringue onto the lined cookie sheet. Clean your spoons between each scoop. Top with a sprinkling of pistachio.
Bake the meringues for 1 hour, then turn off your oven, open it a crack, and allow your meringues to dry out for at least 1 more hour before serving!