Rinse the millet, black rice/black glutinous rice, peanuts, and red beans clean to wash away any dirt or dust. Transfer everything to a thick-bottomed soup pot along with 6-8 cups of water. Soak for 1-2 hours, or overnight.
After soaking, cut the red dates open and remove the pit in the middle. You can use your fingers, or cut around the pit with a paring knife. Add the dates, dried longan fruit (if using), and ginger.
Bring the porridge to a boil, then cover and reduce the heat to low. Simmer for 1 hour. If the soup boils over, slightly angle the lid to release excess steam. Adjust the heat to ensure that the porridge is at a low and slow simmer. Avoid the temptation to stir the porridge, as the grains will stick to the bottom of the pot the more you stir it.
After one hour, turn off the heat, and leave the porridge on the stove for 1 hour, letting it continue cooking in residual heat.
Add the goji berries and the Chinese brown sugar (if using). Bring to a boil, and cook until the porridge reaches the ideal thickness, which should take about 10-15 minutes. Serve hot!
Notes
Note: nutrition information is per serving and includes all ingredients in recipe except the optional sugar.