For the hot cocoa: Whisk all the ingredients (heavy cream, chopped chocolate, milk, vanilla, cocoa powder, pinch of salt) in a saucepan on medium heat until melted, smooth, and slightly thickened.
For the marshmallow meringue: In the bowl of a stand mixer, stir the egg whites and sugar together to combine. Set the bowl over a saucepan filled with about 2.5 cm’s of water and over medium-low heat. Do not let the base of the bowl touch the water. Heat the mixture until it reaches about 150F on a candy thermometer, or until the sugar is fully dissolved and the mixture looks cloudy. Make sure to scrape down the bottom and sides of the bowl to avoid any sugar crystallization.
Once at temperature, remove the bowl from the heat and place it in the stand mixer fitted with the whisk attachment. Set the mixer speed to medium-high. Whisk until the mixture forms stiff and glossy peaks, about 6 minutes. Add in the vanilla bean seeds and salt and continue to whisk until evenly combined, a further 30 seconds. The bowl should be cool to the touch and all the steam will have escaped from the meringue. Stop mixing and remove the bowl from the stand mixer.
Pipe the marshmallow fluff onto the hot chocolate and use a blow torch for the toasted marshmallow effect.
