In a blender, grind the rice with 1 cup of the water, adding more water a tablespoon at a time if needed. Add the sesame seeds or black sesame powder and process until the mixture becomes a chunky paste, adding more water if needed
Put the black rice mixture in a medium pan and stir in the rest of water. Let simmer over medium heat for about 20 minutes, stirring occasionally and breaking up any lumps as needed. Reduce the heat and let simmer and additional 10 to 15 minutes, stirring more frequently as the porridge thickens. It should be the consistency of oatmeal. If it's too thick to your liking, add a bit more water
Divide the porridge among 4 individual bowls. Serve them warm or room temperature with optional toppings suggested above