For many South Asian style curries the base for many dishes is usually the same.
Onions, cooked on a higher heat and constant stirr for a few mins, then lower the heat and cook for longer. And keep stirring. You need more oil than you think and can spoon it out later. The Dishoom cookbook explains this very well, there are 2 pages dedicated to it! This caramelises the onions and adds an incredible depth of flavour.
Garlic and ginger, both as fresh as possible. Finely chopped and added about 5 mins once the onions are in the pan.
Once the onions are cooked we'll only then add tomatoes. If you have time take the seeds out and finely chop. If you have been more time, put the tomatoes whole in hot water for one minute then rinse under cold water. Remove skins then finely chop. Curries made without tomato skins and seeds taste better. You could add a small amount of tomato puree for flavour and sweetness.
Then you have a onion, garlic, ginger and tomato base.
Optional - You can use something like a mashing devise or hand blender to mix into a paste. Restaurants do this a lot.
Then comes the spices which have to be gently cooked.
Spice - buy the best quality you can, I use Barts. If you have time, use whole spices that have been toasted gently on a pan and blend in a spiice blender or coffee grinder. Whole spices add so much flavour and you need less. Or if you're in a hurry, a good quality garam masala mix and coriander seeds ground into a powder using pestle and mortar. There is a world of difference between shop bought corian powder and home made which can be done in less than a minute.
Play around with spices. I find recipe books use a lot more than needed. Some prefer more cumin, some like more garlic etc. go with what works for you but start with smaller amounts.
You know the base is ready when the oil is separating from the base. Then you can add in whichever meat or vegetable you want and cook on a high heat and keep stirring for a few mins then slower to simmer for longer.
My mum used to cater for parties and this was her base for curries which always got reviewed well and was a repeat order for many.