Place all spice paste ingredients into a food processor or blender and pulse until smooth.
In a frying pan, heat the peanut oil over medium heat and fry the spice paste for 2 minutes. Turn off the heat and set aside to cool.
In a large pot over medium-high heat, add the chicken breast and makrut lime leaves, then pour the stock and water over them. The liquid should cover the chicken.
Bring to a boil, cover and reduce the heat to low. Let simmer until the chicken is cooked through, about 5-10 minutes. Remove the chicken from the pot and shred it into small pieces. Set aside.
Skim off any foam in the broth and bring heat to simmer.
Stir the spice paste into the broth. Let it simmer for another 10 minutes. Add the salt and sugar to season. Turn off the heat and strain the broth through a sieve.
Prepare the vermicelli rice noodles by soaking them in boiling water for 2 minutes and strain.
To serve, portion out the cooked noodles and shredded chicken into 4 bowls. Ladle some broth over each and add toppings such as hard-boiled eggs, tomatoes, chopped Chinese celery, chilli, bean sprouts, fried shallots and lime wedges.
