Heat the condensed milk in a pot on the stove and stir with the sugar until it melts. Then, pour in the cocoa and stir until dissolved well.
Remove from the stove, transfer to a suitable bowl and add the butter, stirring. Next, pour in the powdered dry milk and stir with a whisk.
Distribute it into dessert cups and serve with a decoration of your choice or store in a jar in the fridge.