Blend all spice paste ingredients, except curry powder, until smooth. Add some water, if necessary.
Pour mixture into a bowl. Mix with curry powder to form a thick paste.
Heat vegetable oil in a large pot over medium heat. Stir fry spice paste until fragrant, about 5 minutes.
Add chicken thighs and cook until opaque, about 3 minutes.
Pour in water. Cover and bring soup to a boil. Reduce heat and allow it to simmer for 30 minutes.
In the meantime, fill a separate pot half full of water. Bring to a boil. Scald bean sprouts for about 20 seconds. Remove with a metal strainer.
Add dried noodles and cook for 3 to 5 minutes. Remove with metal strainer. Set aside.
Minced fried salted fish. Remove chicken thighs from curry soup with tongs. When cool enough to handle, shred meat and discard skin and bones.
Pour coconut milk into soup. Season with salt. Bring it up to a boil and allow coconut milk to heat through. Turn off stove.
Place a portion of noodles, bean sprouts, some shredded chicken, and 8 to 10 pieces of yong tau foo in a bowl. Pour curry soup over noodles and yong tau foo. Garnish with green onions, fried shallots, and crumbled salted fish.
Serve immediately with a teaspoon of fried chili paste.