Prepare the topping first: Mix grated coconut with salt and steam for 10 minutes. Leave aside to cool. Soak sago for 10 minutes then drain well. Combine sago, tapioca and sweet potato in a large mixing bowl. Add sugar, custard powder and coconut milk and stir well to mix .
Transfer the combined mixture to a 15cm square tray. Level the surface evenly. Steam over high heat for 30-35 minutes or until cooked through. Leave the kuih to cool then cut into slices and coat with the prepared grated coconut .