Warm the milk to a simmer, take off the heat and add the chocolate, whisking all the time until melted. Store in a squeezy bottle.
Warm the brownies in the microwave for 1 minute. Toast the marshmallows with a blow torch or in the flame of the cooker. Zigzag the chocolate sauce over the base of the plate. Add the brownie, stack up the toasted marshmallows and add a ball of icecream. Dust with icing sugar and serve.