Put the curry powder into a large
saucepan, then toast over a medium
heat for 2 mins. Add the olive oil, stirring
as the spice sizzles in the pan. Tip in the
onions, apple, garlic, coriander stalks and
ginger, season, then gently cook for
5 mins, stirring every so often.
Meanwhile, peel, then grate the sweet
potatoes. Tip into the pan with the stock,
lentils, milk and seasoning, then simmer,
covered, for 20 mins. Blend until smooth
using a stick blender. Stir in the lime juice,
check the seasoning and serve, topped
with roughly-chopped coriander leaves.