Start by cooking the yellow noodles according to the package instructions. Drain and set aside.
In a frying pan, heat the cooking oil over medium heat. Add the chopped shallots, ginger, and soaked dried red chillies. Sauté until the shallots are translucent and fragrant.
Stir in the ground coriander, fennel, cumin, and turmeric. Sauté for an additional minute, allowing the spices to bloom.
In a large pot, combine the chicken stock, prawn stock, mashed sweet potatoes, tamarind concentrate, and the sautéed spice mixture. Add the cinnamon stick and bring to a gentle simmer.
After simmering for about 15 minutes, stir in the coconut milk. Let the broth simmer for another 10-15 minutes, adding salt to taste.
To serve, place a generous portion of cooked yellow noodles in a bowl. Ladle the rich broth over the noodles.
Top each bowl with blanched beansprouts, hard-boiled egg halves, fried beancurd slices, prawn fritters if using, and a sprinkle of fried shallots. Garnish with shredded lettuce and lime wedges on the side.