1 tbsp chopped fresh Thai holy basil
1 tbsp chopped fresh coriander
5cm/2in piece galangal, or ginger, peeled, chopped
2 garlic cloves, peeled, roughly chopped
2 stalks lemongrass
1 lime, juice only
1 tbsp chopped fresh mint
3 large baking potatoes, peeled, julienned
4 shallots, preferably Thai, peeled, chopped
400ml/14fl oz coconut milk
salt and freshly ground black pepper
1 tbsp fish sauce
1 tbsp vegetable oil
vegetable oil, for deep frying
1kg/3lb 3oz mussels, beards removed, cleaned (discard any mussels that do not close tightly when tapped gently)
2 fresh lime leaves, roughly chopped
1 tbsp palm sugar