Hot oil. Throw in your cumin seeds and wait till they darken. Blend the onions and cook with the lid on until dark golden brown. Add blended green chillis and ginger/garlic as required and fry off for a couple of minutes. Add meat at this point (if using) which may or may not have been marinated in yogurt/spice mix. Cook off till the oil separates (you are not really getting a sear like in western cooking though). Add tomatoes (canned and blended in my opinion) and water as necessary. Add dry spices at this point and cook for as long as needed.
This is basis for many tomato based curries. Cooking at each stage until the oil separates is the key in my opinion. And go easy on the yogurt – you don’t need much.
What’s great about curries is that there’s no much chopping to be done if you have a food processor.