Pour rice into a medium bowl. Add enough tap water to submerge rice by 1 inch and rub with your fingers to loosen excess starch, making the water look milky. Pour out the water and repeat this process two more times. Finally, add enough filtered water (of the 13 cups listed) to submerge the rice and set it on the counter for 1 hour.
Meanwhile, combine equal parts minced garlic and ginger, minced Thai chili(es), fish sauce, lime juice, and sugar. Stir until the sugar is dissolved and set aside. Note that Thai chilies can be very spicy, so add it in small amounts to taste.
Add a whole pheasant, the remaining water (about 12 cups), and onion halves in a soup pot and bring the pot to a simmer. Gently cook the pheasant until the breasts reach 145° Fahrenheit, about 15 minutes. Debone the pheasant breasts and refrigerate, covered. Return the breast and backbones, wings, and legs to the pot and continue simmering, partially covered with a lid, until the legs become tender, about 1 hour and 30 minutes.
In a small saucepan, heat the duck fat and fry the minced shallot until browned but not burnt. Pour this fat and onion mixture into the pot, along with the rice and soaking water. Bring to a moderate boil and cook for 5 minutes. Then turn off the heat, cover the pot, and allow it to sit for 45 minutes to 1 hour.
Shred the meat off leg bones and return to the pot. Discard the bones and onion halves. Lightly season porridge with salt and white pepper. Reheat the soup and add more water/chicken stock as needed. Ladle the soup into bowls, garnish with shredded pheasant breasts, chopped Vietnamese coriander leaves, and season to taste with a drizzle of the ginger-garlic sauce.
