Preheat the oven to 180°C.
Mix together the sauce ingredients (except the coriander leaves) in a saucepan over a medium heat.
Bring just to the boil, stirring,constantly then remove from heat, stir in the coriander and allow to infuse..
Meanwhile, boil the potatoes,then simmer for 12-15 minutes Drain,and mash them smooth with the butter and milk.Season to taste.
Spread the filling across a suitable (about 1¼ litre) baking dish.
Having removed the lemongrass and whole kafir leaves from the sauce, pour it over the filling.
Smooth the topping over, then add some dots of sunflower spread and rake the surface with a fork.
Cook in the oven 30 minutes then serve with green vegetables of your choice.