How to Make It
Carve the eyes, nose, and mouth in the center of each orange with the tip of a paring knife. Use the tip of the knife to lift the skin off, leaving the pith intact (so that the granita doesn’t melt out). Cut the top quarter off the orange (a little above the eyes) and shave a small slice off of the bottom (this will help them stand up easily).
Loosen the flesh of the orange by running a paring knife around the edge. Scoop out the flesh with a spoon; reserve. Place the empty shells on a sheet tray and freeze until firm, 45 to 60 minutes.
Strain the reserved flesh through a fine mesh sieve, pressing to extract as much juice as possible. Whisk together the sugar and 1 tablespoon hot water until the sugar is dissolved. Combine strained juice, sugar water, and as much orange juice as needed to get to 2 cups in a measuring cup. Transfer the mixture to a 9-by-13-inch dish and freeze until firm, 2 to 3 hours. Scrape the frozen juice with a fork to create small flakes.
Scoop the granita (approximately ¼ cup each) into the frozen shells. Garnish with mint and serve immediately.