Grind spice paste ingredients in a blender or food processor with 2 tablespoons of water.
Heat oil in a medium sized pot and stir fry ground spice paste until fragrant, about 5 minutes. Add chicken and stir till chicken turns opaque, about 3 minutes.
Pour in coconut cream and water**. Add kaffir lime leaves and assam gelugor, if using. When it comes to a boil, season with salt. Reduce heat and let simmer for 15 minutes.
Add cubed potatoes and continue to cook for another 15 minutes, until potatoes are tender, and gravy has thicken.
If you did not use assam gelugor, stir in lime juice now. Turn off heat and allow curry to sit for 15 minutes before serving.
Notes
**Instead of ½ cup (120ml) coconut cream and ½ cup (120ml) water, you can simply use 1 cup (240ml) coconut milk.