Mix the filling ingredients except the butter, lemon juice and chopped herbs and fry in the butter until just cooked through. Sprinkle on approx. 2 tbsp of water and increase the heat until the liquid has evaporated. Remove from the heat and add the lemon juice and herbs. Stir well and leave to cool. Heat oil for deep frying to fairly hot and fry the samosas, several at a time, until golden and crisp. Serve hot with fresh mint chutney