Combine black coffee and sugar until the sugar melts.
Pour mixture into a medium glass pan and place on level shelf in the freezer for about 20 minutes.
When the mixture starts to freeze around the edges of the dish, stir it with a fork, then return the dish to the freezer.
Stir the granita every 20 to 25 minutes until the grains are completely frozen and the texture is fluffy.
Scoop into serving cups and top with sweet condensed milk.