Combine the marshmallow mix and boiling water in the bowl of a stand mixer, whisking slowly by hand until the mix has dissolved. With the whisk attachment, whip the mixture on low speed for 2 minutes, then increase the speed to high and continue to whip for 8 minutes.
Pipe the Chocolate Ganache Filling on the bottom of each tartlet, using a star tip. Then pipe the Marshmallow on top, using an open round tip. Garnish with caramelized cocoa nibs.
