add the onions to the spice tempering. A large pinch of salt helps to draw out the water. Cook over a very low flame until translucent and lightly browned (15-20 mins)
Add the garlic (and ginger, if using). Cook for a further 10 minutes, adding a splash of water to avoid sticking, charring or burning. Cook the onions until until they have completely collapsed and caramelization and umami permeate your kitchen
add the capsicums, with a drop more oil if necessary, and sauté until they begin to soften and change colour
add all the powdered spices, mix into the onions-capsicums and sauté for a good half a minute, stirring continuously
add the tomatoes, season with salt, and simmer until the tomatoes have wilted and the spices have lost their raw aroma. If the masala starts to dry and the spices are still smelling a bit raw, add a splash of water
NOTE some cooks look out for the point where the oil separates from the masala. While this is a sure sign your masala is ready, I find you have you use a good amount of oil for this to work. If you want to moderate your oil use, let your nose be your guide
when the masala is ready, stir in the yoghurt, if using, and finally add in the aubergines:
add a scant cup of water (you can add more later), cover with a lid, and simmer until the aubergines are tender but still hold their shape