Create paste in food processor or mortar & pestle; blend until smooth.
Heat up a heavy bottom pot, and add oil (approximately 1-2 minutes). Tip: use a pot with similar size to the chicken, slightly taller. Lower the heat, fry paste, lemongrass, galangal and kaffir lime leaves until fragrant (approximately 5-8 minutes).Tip: you can add more oil and lower heat if paste starts sticking to pot.
Add hot water and mix well.
Add chicken, make sure it's well submerged.
Simmer on low heat (with lid on) until chicken is cooked (approximately 30-40 minutes).
Take out chicken, drain and let it cool; then cut it into 4 pieces and shred.
Season soup with salt, pepper, sugar and chicken powder (optional).
To serve: add cabbage and shredded chicken into a bowl, and then laddle in soup.
Top with potato cake, egg and sambal.
Garnish with fried shallots, spring onion and celery leaves.