1 1/2 pounds medium shrimp—shelled and deveined, shells reserved
1 onion, quartered
1 carrot, sliced
3 large shallots, quartered
4 jalapeños, seeded and coarsely chopped
1/3 cup thinly sliced fresh ginger
1/4 cup macadamia nuts
1 teaspoon ground coriander
1/2 teaspoon ground turmeric
1/4 cup Asian fish sauce
1/4 cup canola oil
2 plump lemongrass stalks—bottom 8 inches only, outer layer removed, stalk cut into 2-inch lengths
One 14 1/2-ounce can unsweetened coconut milk
2 tablespoons light brown sugar
1 pound Thai flat rice noodles (pad thai), soaked in warm water for 10 minutes
Salt
Lime wedges, for serving