Put 350 g of sugar in a saucepan, add 100 ml of water and allow to caramelize. When the syrup takes on a uniform amber color, add 30 ml of vinegar and 200 g of cream. Cook again for 1 minute and let the butterscotch cool down for about an hour.
Put a generous layer of butterscotch on the bottom of a glass, heat 150 ml of milk without boiling it and emulsify it with a hand blender or a piston coffee maker. This will result in a soft foam.
Prepare the coffee and, once ready, pour the milk into the glass first and then the equivalent of an espresso cup.