Make the spice mix.
Pre-cook the coarsely chopped onion. Heat your skillet over medium heat. Add 1 Tbsp vegetable oil and fry the onions until the edges just start to turn brown. Remove onions but leave the oil in the pan.
Dilute the tomato paste with enough water to get to the consistency of passata.
Heat your frying pan (don't use non-stick) briefly over medium heat. Add the rest of the oil. Use all the oil specified. It's important.
When the oil starts to shimmer add the finely diced onion and and stir every few seconds until the onion is soft and starts to brown, about 3 minutes. If you are using the optional coarsely chopped green chili add it in after 2 minutes (so it cooks one minute).
Next comes the garlic ginger paste. Add it into the pan and cook it, stirring constantly, until it stops sputtering.
Stir in the green chili and minced cilantro stems and stir. Cook for another 15-20 seconds.
Turn down the heat and add the spice mix. This is the critical step. Stir it constantly for 30 seconds. If it starts to darken lift the pan off the heat. You want the spice mix to cook in the oil but not burn.
Turn the heat up to medium high. Add the diluted tomato paste and stir until bubbles form (the oil will likely separate). This takes around 30 seconds to one minute depending on the heat.
Add 3 oz of curry base. Stir until bubbles form (little craters really), around 30 seconds. Watch the edges of the pan. The curry can stick here.
Now add 6 oz of curry base and stir briefly. Let it cook until the bubbles form again. This takes 1-2 minutes.
Add the rest of the curry base and let cook until the bubbles form. Turn the heat down to low and add the pre-cooked lamb, beef or chicken, the pre-cooked onions and the sugar.
Let the curry simmer for about 5 minutes. If it gets too thick add a bit more curry base. Don't add water.
Garnish with a bit of chopped fresh cilantro and serve.