Peel the mango using a sharp paring knife to remove only the thin outer skin.

Score both sides of the mango flesh down to the core in a grid pattern. Slice the pieces away from the pit, cutting as close to the center as possible to maximize the yield, then scrape any remaining pulp from the pit.

Place the mango flesh in a blender and process until completely smooth. Stream in water one spoonful at a time until the mixture reaches a fluid, smoothie-like consistency.

Taste the purée and add a pinch of sugar if the fruit isn't at peak sweetness, then transfer to a container and chill thoroughly in the refrigerator.

Toast the cumin seeds in a small pan over medium heat, stirring frequently. They are ready when they turn a deep brown and smell intensely nutty, usually after 3 to 5 minutes.

Grind the cooled seeds into a coarse powder using a mortar and pestle or spice grinder. Serve the chilled ras in small bowls, topped with a dusting of the toasted cumin and ground ginger.