In reply to goldmember:
Onion, ginger, garlic into a blender with a little water.
Fry this mix in an obscene amount of ghee with black mustard seeds, tandoori spice mix and chilli (sounds odd frying a liquid, but trust me!)
Add potatoes diced to about 1.5cm and continue to fry until liquid begins to coat the potatoes.
Transfer to a couple of large baking sheets and place in hot oven.
Turn regularly and apply more ghee as necessary.
A little labour intensive, but worth it!