Place the ginger and shallots directly over the burner grate of the gas stove for about 5 minutes making sure to char all the sides.
Rinse the chicken and pat it dry with paper towel.
Season the skin and cavity of the chicken with salt and pepper. Tuck in the legs and wings so it fits snugly in the pot. Place the chicken breast down in the inner pot of the pressure cooker.
Place the scallions, charred shallots and ginger in the inner pot. Add 12 cups of water making sure the water level doesn't go above the maximum fill line. Take out some water if necessary. Add salt, fish sauce, and sugar.
Lock the lid and pressure cook on HIGH pressure for 10 minutes. Let the steam naturally release for 10 minutes before manually releasing the rest.
Remove the chicken from the pot and let it rest until cool enough to handle. Pull the chicken from the bones and place the meat on a plate and set aside. Discard all the solids.
Place the glass noodles in a large bowl and pour enough hot water to cover the noodles. Let them soak for 10 minutes. Drain and snip the noodles with kitchen shears into 6 inch lengths.
Taste the broth and season with additional fish sauce and sugar to your liking.
When ready to serve, divide the noodles among serving bowls and add shredded chicken.
Ladle the soup into the bowls. Garnish with green scallions, cilantro, fried shallots, and a sprinkle of freshly ground pepper. Serve immediately.