Bring thickened cream and evaporated milk to boil in a saucepan. Mix in chocolate, leave to stand for one minute and then stir until mixture is completely smooth. Transfer to a large bowl.
Using the same saucepan, bring milk and water to a boil, then add the chocolate spice. Whisk mixture until no lumps remain.
Pour the chocolate spice mixture into the bowl containing cream and milk. Stir until everything is combined.
For the spiced marshmallows
Sprinkle gelatin powder into the first ¼ cup of cold water and let stand to soften, about 1-2 minutes.
Bring the sugar, glucose syrup, the second ¼ cup of water and the chai masala spice to boil in a saucepan. Insert the sugar thermometer and bring the temperature up to the range of 115-120°C, the soft ball stage.
Pour over the gelatin mixture, stirring until the gelatin dissolves. In a stand mixer with the whisk attachment, or in a deep bowl if you are using electric hand beaters, whisk until the mixture is triple in volume and lukewarm to the touch, around 6 minutes.
In a separate bowl, whisk egg white to stiff peaks. Please make sure that your bowl and beaters are scrupulously clean for this step. Fold egg white into the other mixture and spread evenly on a well-oiled pan lined with baking paper. Leave overnight to set completely. Cut into cubes and serve in the hot chocolate.
Hot chocolate keeps very well in the fridge, to be reheated at a moment’s notice for instant comfort that comes in a cup.