Heat 2 cups of water on the stove until it’s just warm, then whisk in the cocoa powder, sugar, and salt until everything has dissolved. Let cool to room temperature, then pour into an 8x8-inch baking pan. Freeze for 45 minutes to 1 hour, until the perimeter is starting to freeze. Remove the pan from the freezer and use a fork to scrape the frozen edges toward the center and shuffle everything around. Freeze for another 30 minutes, then scrape and shuffle with the fork again. Repeat this—mixing every 30 minutes—until the granita is totally frozen and snowy in texture (this will take anywhere from 2 to 3 hours total, depending on your freezer). At this point, you can eat right away, or transfer to airtight containers and store in the freezer for up to a couple weeks.
When you’re ready to dig in, spoon some granita into a dish and top with whatever rich ingredient you have around—sweetened condensed milk, whipped cream, Greek yogurt, crème fraîche, or even a drizzle of extra-virgin olive oil are all wonderful. A pinch of flaky salt on top is nice, too.