Dissolve the sugar over a bain-marie

• Add the aquafaba and sugar to a heat-safe bowl and set it over a pot of gently simmering water, making sure the bowl doesn't touch the water.
• Whisk constantly until the sugar is fully dissolved; a drop rubbed between your fingers should feel completely smooth with no graininess.

Whip the fluff

• Transfer the mixture to a mixer, add the cream of tartar and whip on high speed until thick, glossy and holding stiff peaks.
• The bowl should feel cool and the texture should look smooth and marshmallowy.

Pipe and toast the marshmallow ring

• Transfer the fluff to a piping bag and pipe a ring around your mug.
• Torch the fluff until toasted.

Serve

• Pour the hot chocolate into the mug and let the marshmallow melt in.