In saucepan over medium heat, toast red spur chilies in butter until browned and fragrant, then remove chilies from butter, add garlic and shallot, continue toasting until fully golden brown and fragrant, then add bay spice, toast 30 seconds further until browned and fragrant, then add prawn stock, lemongrass, and coriander root.

Reduce over medium heat by about two thirds, then remove lemongrass and coriander root, transfer to blender, blend over high speed, taste and adjust as needed.