Thai Panang Curry Paste

7 dried spur chiles (about 9g total), stemmed and seeded (see note)
2 stalks lemongrass, bottom 4 to 5 inches only, outer leaves discarded, tender core thinly sliced (about 20g sliced lemongrass)
one 2 ½-inch piece fresh galangal, peeled and thinly sliced (about 1 tablespoon; 10g; see note)
1 ½ teaspoons (3g) finely grated makrut lime zest from 3 makrut limes (optional, see note)
2 coriander roots (8g), cleaned and thinly sliced (see note)
2 garlic cloves (10g), thinly sliced
1 small shallot (20g), thinly sliced
1 teaspoon (10g) Thai shrimp paste
2 tablespoons (25g) roasted unsalted peanuts
½ piece (6g) whole nutmeg
2 teaspoons (4g) whole coriander seeds
½ teaspoon whole cumin seeds
½ teaspoon white peppercorns

Cut dried chiles into ¼-inch pieces with kitchen shears and soak in warm water until softened, about 20 minutes. Drain well in a sieve.
While chiles soak, toast coriander in a dry small heavy skillet over moderate heat, shaking skillet, until fragrant, 3 to 4 minutes, then cool. Thinly slice lower 6 inches of lemongrass stalks and finely chop.
Finely grind coriander and peppercorns with mortar and pestle (or in mini food processor), about 2 minutes, then toss together with lemongrass, galangal, lime leaves, cilantro, shallot, garlic, fresh chiles, and soaked dried chiles in a bowl.
Pound mixture in 3 batches with mortar and pestle until a fairly smooth paste is formed, 8 to 10 minutes per batch, transferring to cleaned bowl. (If using food processor, add about 1 ½ tablespoons water per batch.)
Return all of curry paste to mortar, then add shrimp paste and salt and pound (or pulse) until combined well, about 1 minute.