Scrub potatoes and remove skin and chop to pieces and place in a pot of water. Boil potatoes until softened and mash till smooth.
Cut tau kwa to small cubes and shallow fry till golden brown set aside.
Heat up 2 tbsp of oil in wok. Add in pounded lemongrass and galangal and fry together with fermented soy bean paste.
Add coconut milk, stir fry well for about 3 minutes at medium heat.
Add sugar, chicken stock, dark soya sauce and curry powder, stir well and add in 600 ml water.
Add in mashed potatoes and stir gravy until smooth with a hand whisk and simmer for about 10 minutes.
If you find the gravy is still too thick, add a little more water to it or mix some corn starch with little water as thickening if the gravy is too watery.
To serve, blanch yellow noodles and bean sprouts in boiling water, drain well and place in serving bowl.
Spoon the hot gravy over the noodles and garnish