Fry the potato slices on medium heat until done. Remove and drain then blot on tissues. Alternatively you can boil the potatoes whilst whole and then peel and slice them for a healthier version, but it won't taste as good as the fried ones. ;)
Wash and cut the tomatoes into quarters (skin and all!). Put them in a blender, add the 2 green chillies and a bit of the coriander stems for extra flavour. Add a bit of water and blend until completely smooth.
Heat some oil in a pan or wok. Add the garlic paste, followed by the tomato paste. Let this fry for a couple of minutes on low whilst stirring regularly, then add the turmeric and blended tomatoes. Sprinkle some salt, cover and let this simmer on medium heat until it thickens and the tomatoes' raw taste has gone. Add the tsp. of sugar and keep simmering for a few more minutes until it thickens to a lovely gravy n some oil begins to separate from it.
Now add the fried potatoes and stir together, adjust salt and if you prefer the gravy to be a bit lighter you can add a bit of water and simmer it for a few minutes. The potatoes will absorb some of the moisture, so make sure that there is a bit more gravy than you would normally want, some will disappear into the potatoes.
Garnish with coriander leaves and serve!
If you're using boiled potato slices, after you add them into the gravy, spread out everything on a greased tray and stick it in the oven for about 5 minutes to give it a nice finish.