Place the sugar in a small pan, add the water and wait for it to caramelise. When the syrup turns an even amber colour, add the vinegar and the double cream. Cook for one more minute, and then let the cream cool for around one hour.
Put a generous layer of toffee cream in the bottom of the glass. Heat the milk without bringing it to the boil and emulsify it with a hand blender or a French press to produce a frothy foam. Make the coffee and, when ready, pour the milk into the glass first, followed by the equivalent of a shot of coffee.
Create a spiral on the surface of the milk and use a toothpick to draw a cobweb.