In a bowl, stir together the coffee, sugar, vanilla and salt until the sugar dissolves. Pour into an 8-inch square baking dish and place in the freezer for 2 hours. Remove from the freezer and use a fork to scrape any of the ice that has formed.
Return to the freezer for another 2 hours, then repeat the scraping. If the granita is still not frozen, return to the freezer again and repeat the scraping. Serve with a dollop of whipped cream on top or drowned with 1/2 ounce of limoncello.