To make the nam prik, put the galangal and garlic into the small bowl of a food processor and blitz until finely chopped but not completely smooth. Transfer to a small bowl and set aside until ready to serve.
Toss the cabbage with the oil and 1 teaspoon of flaked salt. Place on a very hot barbecue or griddle pan and grill for 4-5 minutes on each side (i.e. 12-15 minutes in total), until the cabbage softens on the outside, while still retaining a crunch, and you get clear grill marks. Transfer to a platter.
Add the corainder to the nam prik and spoon the mixture evenly over the cabbage pieces. Serve either warm or at room temperature, with the lime wedges alongside.
