Boil egg noodles in salted water until tender, drain and set aside. Cook vermicelli by soaking in boiling water for 3-4 minutes. Drain and set aside.
In a mortar and pestle, grind paste ingredients to smooth paste.
Make shrimp oil by nipping tails off prawns and frying in 2-3 tablespoons of oil until golden. Remove shells and add the shrimp-flavoured oil to the paste.
Heat oil in large pot and fry paste until fragrant and beginning to brown. Add stock, lemongrass, chicken, and coconut milk, bring to a simmer and cook for 10 minutes.
Add prawns and simmer until they, and the chicken, are cooked though. Taste and add salt if required. Add juice of lime.
Divide noodles and vermicelli evenly into 4 bowls. Spoon chicken and prawns into each, then pour hot laksa broth over and garnish.