Use kitchen shears to chop chili peppers into large pieces (about 4 pieces per pepper). Shake the seeds out of the peppers (the more seeds you remove the less spicy the curry paste will be). Soak peppers in warm water for 10 minutes to soften.
While peppers soak, place shrimp paste on a small piece of foil and then fold the foil up to form a packet that completely encloses the shrimp paste.
Heat a skillet over medium-high heat. Place shrimp paste packet onto heated skillet and toast for about 2 to 3 minutes on each side, until fragrant. Set aside.
Return skillet to medium-high heat and add coriander seeds, cumin seeds, and white peppercorns. Toast spices, stirring constantly, until fragrant, 4 to 5 minutes.
Grind coriander seeds, cumin seeds, and white peppercorn using a mortar and pestle or spice grinder until they form a fine powder. Set ground spices aside. (Note: if you don’t have a mortar and pestle or a dedicated spice grinder, you can also pulse the dried spices in the blender or food processor, but it may take up to 10 minutes of blending / pulsing until a fine powder forms.)
Return to dried peppers and drain off as much water as possible.
If using a mortar and pestle:Combine soaked chili peppers and salt in a mortar and pestle and grind until smooth.Add lemongrass, galangal, shallots, garlic, and cilantro root. Grind again until smooth.Add shrimp paste and dried spices. Continue to grind / mix everything together until even. If using a blender or food processor:In a blender or food processor, combine chili peppers, lemongrass, galangal, shallots, garlic, cilantro root, and shrimp paste. Blend until the mixture forms a paste that still has a small amount of texture, pausing to scrape down the sides as needed. (Note: if the mixture does not blend easily, add water a bit at a time, as needed, to help it blend.)Add dried spices and salt and blend just until the spices are fully mixed in.
Taste curry paste and season with some additional salt, if needed.
Curry paste can be stored in the refrigerator for about 1 week or frozen for up to a year.