Add butter and olive oil to a heated pot.
Add chicken and brown on both sides.
Add carrots and onion and saute for 3 minutes.
Add garlic, lemongrass, ginger, salt and pepper.
Add chicken stock and fish sauce.
Bring to a boil, and then reduce heat and allow to simmer for 20- 30 minutes, or until vegetables are soft.
Remove chicken thighs and either shred or cut into bite-sized pieces. Return chicken to soup.
Add coconut milk.
If using noodles, place noodles in individual bowls, and ladle soup on top.
Top with chopped cilantro if desired.