Soak dry chillies in hot water for about 10 minutes to soften it. Keep the chilli water for blending later.
Peel and cut garlic, shallots, galangal into smaller pieces. The smaller the better.
Remove stem from kaffir lime leaves, stack all the leaves together and roll them like a cigar. Slice the leaves thinly.
Remove both ends and the outer layers of lemongrass. Bruise the lemongrass by hitting it with the back of the knife. Slice the lemongrass thinly.
Cut the softened dry chillies into smaller pieces.
Grind the cumin seeds and coriander seeds in the blender. If you are using cumin powder and coriander powder, you can skip this step and just add the powder to the ingredients for blending.
Add all ingredients into the blender - chilli, garlic, shallots, galangal, lemongrass, cumin powder (or ground cumin seeds), coriander powder (or ground coriander seeds), shrimp paste.
Add about 3-4 tbsp of the chilli water.
Start blending at high speed.
Add more chilli water according to the dryness of the paste to make it easier to blend, if necessary.
Once paste is consistently blended and quite smooth, the paste is ready.