Pat the chicken thighs dry with paper towels and season all over with salt and white pepper. Place them on a plate, skin side up, and transfer to the fridge for 2 hours uncovered.
Separate the dark green parts of the scallions from the white/light green parts and set aside for later. Remove the root ends from the whites and discard them. Cut the white/light green parts into thin matchsticks and set aside. Thinly slice the dark green parts for garnish. Peel the ginger and cut it into thin matchsticks.
Place the rice in a fine mesh strainer and rinse with cold water until the water runs completely clear. Set aside to dry.
Heat the oil in a 5-6 quart dutch oven over medium-low heat. Place the chicken thighs into the pot skin side down. Cook for 5-6 minutes until some of the fat has rendered. Transfer the chicken back to the place, skin side up, and let cool slightly. Remove the skin from the thighs and place it on a parchment lined baking sheet.
Remove all but 1 tablespoon of the fat from the pot and discard. Add the thinly sliced ginger and scallions (white/light green parts) and cook for 2 minutes, stirring often, until fragrant. Stir in the rice and cook for another minute, tossing well. Stir in the chicken stock and sesame oil, and return the chicken thighs to the pot. Bring to a boil, reduce to low, cover, and simmer for 1 hour, stirring every 15 minutes.
Preheat the oven to 350 F. Transfer the baking sheet with the chicken skin to the oven for 20 minutes, or until golden and crispy. Transfer the chicken skin to a paper towel lined plate.
After an hour, remove the chicken thighs from the pot and continue to cook the rice covered for 30 more minutes. Shred the chicken meat off the bones and return it to the pot. Season to taste with salt or soy sauce and white pepper.
Ladle the congee into bowls and top with the crispy chicken skin, sliced scallions, and any additional toppings as desired.