Stir sugar and coffee until the sugar is dissolved. Pour coffee into a flat form and place in the freezer for about 4 hours.
Whip the cream until stiff. Mix mascarpone, sugar, orange peel and orange juice. Fold in the cream. Pour mascarpone cream into four glasses (250 ml each) and chill until serving.
Scrape the coffee granite out of the mould with a tablespoon and pour it onto the cream. Serve immediately.