Step 1

Bring stock to the boil over high heat in a very large saucepan, add chicken and lemongrass, and bring back to the boil, then reduce heat to low-medium, simmer for 10 minutes, then turn off heat, cover with a lid and leave to continue cooking chicken in stock until juices run clear when pierced with a skewer (1½ hours). Remove chicken from stock and, when cool enough to handle, tear meat into bite-size pieces. Strain stock, return to saucepan with chicken meat, season to taste and set aside.

Step 2

Dry-roast chillies over medium-high heat until fragrant and toasted (30-40 seconds) and reserve for serving. Dry-roast whole spices in same pan until fragrant (10-20 seconds), finely grind with a mortar and pestle, then add shallots, ginger, turmeric and a pinch of salt and pound to a smooth paste. Reserve.

Step 3

Place noodles in a large heatproof bowl. Cover with boiling water and stand until cooked al dente (2-4 minutes). Drain and leave to cool slightly, then chop with scissors into serving bowls.

Step 4

For fried shallots and garlic, heat 5cm oil in a wok or small saucepan over medium-high heat until it shimmers. Add shallots and stir-fry until golden brown and crisp (1-2 minutes). Remove with a slotted spoon and drain on paper towels, then repeat with garlic. Strain and reserve oil.

Step 5

Heat 1 tbsp reserved shallot oil in a frying pan over medium heat, add shallot paste and stir continuously until fragrant (1-2 minutes). Add to chicken broth, bring to the boil, season to taste with fish sauce and lime juice, then pour into bowls over vermicelli noodles. Scatter with dry-roasted chilli, fried shallots and garlic and herbs, drizzle with shallot oil to taste (see note) and serve with lime wedges.