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 to dried peppers and drain off as much water as possible.
If using white peppercorns, grind them to a fine powder in a mortar and pestle or spice grinder. (You can skip this step if you are using pre-ground white pepper.)
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 ground white peppercorn. Continue to grind / mix everything together until even. If using a blender or food processor:In a blender or food processor, combine soaked chili peppers, salt, ground white peppercorn, lemongrass, galangal, shallots, garlic, and cilantro root. 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.)
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.