5 Thai chiles, seeded and chopped
4 stalks of fresh lemongrass, tender inner bulb only, finely chopped
4 garlic cloves, coarsely chopped
1/3 cup coarsely chopped peeled fresh ginger
1 large shallot, coarsely chopped
1 tablespoon coconut oil (see Note) or vegetable oil
3 1/2 cups unsweetened coconut milk
1/4 cup plus 2 tablespoons dark brown sugar
1/4 cup Asian fish sauce
1/4 cup tamarind concentrate (see Note)
6 fresh kaffir lime leaves (see Note)
3 tablespoons fresh lime juice
Salt and freshly ground pepper
3/4 pound medium shrimp, shelled and deveined
Cooked rice vermicelli or steamed rice, for serving (optional)