Set pan of frozen espresso on a cool surface and methodically chop the crystalline blocks into a regular flaky, granular mass. This can be tedious, but it is easy, as long as you haven't let the liquid freeze too solid. If it is rock hard, it will take more brawn to cut through chunks and you may overwork some bits as you try to split harder pebbles. At opposite extreme, in rare instances where mixture is fairly sweet or thick, it may never fully freeze hard and will chop to a rich, grainy-slushy texture. Such "defective" granitas can be exquisite. Transfer granita to chilled container, snap on lid and place in freezer.
Ten to 15 minutes before serving, turn container upside down in freezer (espresso syrup sometimes drains from ice crystals, like syrup in a snow cone; turning it upside down will redistribute the syrup). Place 5-to 6-ounce bowls or glasses in freezer to chill. I use clear, narrow, fluted stemware to show off the layers and crystals.
Take the cold, medium-size bowl from the freezer, combine cream and sugar and whip until stiff. To serve, layer granita and whipped cream like a parfait in chilled glasses. There should be nearly as much whipped cream as granita. The cream's surface will freeze where it touches the granita, and the succession of voluptuous chewy and slushy textures is delightful.
The owner of this pot de creme cup describes it as being from the Napoleon III era from the Sevres factory in France