Put the sugar, cornstarch and instant coffee in a container or even directly in a large saucepan.
Mix and pour in the milk little by little while whisking.
Heat over moderate heat, whisking continuously.
The cream will thicken after about 10 minutes. Bring it to a boil.
When the cream boils, pour it into a clean container.
Filter directly on contact with a heat-resistant film.
Let cool at room temperature and then at least 4 hours in the refrigerator, preferably overnight. Then remove the cling film, and that's when the magic happens! Blend the cream in a hand blender. The cream will become smooth and shiny.
Put it back in the fridge, still with the cling film in place, and enjoy it cold!