A cheat's pudding and glorious it is too. If you don't have time to make your own brownies, use ready-made. Try using white chocolate for the sauce, too.
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.