The secret to a good curry sauce is the onions.
Use twice as many as you think you need. Cook on a lowish heat as follows: use a relatively small amount of rape seed oil. Turn the onions in the oil to coat them fully. When they begin to soften, add a small splash of water. SMALL, I said, don't drown them. Keep stirring gently all the time. Cook off the water and repeat. Keep adding water and cooking it off until the onions become jammy. JAMMINESS is all. They should not caramelise too much, i.e. brown bits at a minimum. Now you can make any curry you like by adding your spices, cook at a low heat adding one small splash of water until the spices are fragrant. Voila, perfect curry base. Choice of spices depends on personal taste and the type of dish, but these provide a good general base: turmeric, cumin, ground coriander, garam masala (not classical, but a fragrant mixture), a little tomato puree, mustard seed (not too many), a few fennel seeds, garlic and fresh chillies. Fresh coriander is a minority taste. Maybe add fresh ginger (never powder).
