A sugar syrup mixed with coffee, frozen, and raked with a fork every time it starts to set until it turns to loose crystals. Two ingredients and a freezer, and the raking is the whole recipe.
The raking is the recipe. A granizado is not frozen and then crushed: it is scraped with a fork every time a layer starts to set, so the ice grows as separate crystals instead of a solid block. Skip a round and you get a slab you cannot get a spoon into. Expect to do it three or four times over several hours, roughly every forty minutes, and to leave it overnight if you want it ready in the morning. A shallow dish freezes faster and more evenly than a deep one. The ingredient list has two quantities of water and only the three glasses are used in any step, for the syrup. The 500 ml never appears again, and the likeliest explanation is that it is the water for brewing the coffee, since the coffee arrives in the second step without any. The recipe does not say, so it has been left in the list as it was.