Heat oil in deep frying pan or wok for about 1 minute, add diced potatoes, stir in until edges go transparent (about 2-3 minutes) and add aubergine cubes. Stir and cook until aubergine squares start to brown.
Add turmeric, stir, then crush cumin and coriander seeds in mortar or grinder and add, stir in, along with chili pepper, if used.
Add salt, then about half the water (1 cup), to just cover the aubergine and potato cubes. Squeeze in lemon juice and bury the rind in the middle of the mix (this gives the curry a slightly bitter flavour).
Cover and simmer for about 20 minutes until potatoes are tender, stirring occasoinally. Add more water as needed to keep mix just covered. Add and stir in curry powder or Garam Masala just before serving.
No Indian meal is complete without this excellent side dish:.
Make up yeast with hot-to-the-finger water, sugar and a tbs of the flour. Leave to froth up (5-10 mins), meanwhile, put most of the rest of the flour and salt in a bowl, make a well in the centre and add the oil. Rub in with fingertips, then add the yoghurt and stir inches Add the yeast mixture slowly and stir with a spoon handle until the dough makes a ball, then sprinkle on last of the flour to make a firm dough which does not stick to the fingers (you may need to add some more flour at this point to make this happen). The dough does not need to be kneaded, but should form into a well-shaped ball in the hands. Leave to rise for about half an hour in a warm place, then divide into 4 evenly-sized balls. Work each one into an oval of about 4x8 ins with the hand, or using a rolling pin then in turn slap onto a very hot griddle or bottom of a good frying pan. The bread will rise quickly and begin to bubble up. Turn over when it is starting to turn golden underneath, and cook the other side for another minute or so, trying not to burn the tops of the bubbles too much.
Add ingredients to the chilled yoghurt, stir inches Serve the Potato and Aubergine curry in a ring of rice, with 1-2 tsp of this dressing in the middle.